Fin strain in quantum dot devices

ABSTRACT

Disclosed herein are quantum dot devices, as well as related computing devices and methods. For example, in some embodiments, a quantum dot device may include: a base; a fin extending away from the base, wherein the fin includes a quantum well layer; a gate above the fin; and a material on side faces of the fin; wherein the fin has a width between its side faces, and the fin is strained in the direction of the width.

BACKGROUND

Quantum computing refers to the field of research related to computationsystems that use quantum mechanical phenomena to manipulate data. Thesequantum mechanical phenomena, such as superposition (in which a quantumvariable can simultaneously exist in multiple different states) andentanglement (in which multiple quantum variables have related statesirrespective of the distance between them in space or time), do not haveanalogs in the world of classical computing, and thus cannot beimplemented with classical computing devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detaileddescription in conjunction with the accompanying drawings. To facilitatethis description, like reference numerals designate like structuralelements. Embodiments are illustrated by way of example, not by way oflimitation, in the figures of the accompanying drawings.

FIGS. 1A-1B and 2-3 are cross-sectional views of a quantum dot device,in accordance with various embodiments.

FIGS. 4-33 illustrate various example stages in the manufacture of aquantum dot device, in accordance with various embodiments.

FIGS. 34-36 are cross-sectional views of another quantum dot device, inaccordance with various embodiments.

FIGS. 37-39 are cross-sectional views of example quantum well stacks andsubstrates that may be used in a quantum dot device, in accordance withvarious embodiments.

FIGS. 40-46 illustrate example base/fin arrangements that may be used ina quantum dot device, in accordance with various embodiments.

FIG. 47 is a cross-sectional view of another quantum dot device, inaccordance with various embodiments.

FIG. 48 illustrates an embodiment of a quantum dot device havingmultiple trenches arranged in a two-dimensional array, in accordancewith various embodiments.

FIG. 49 illustrates an embodiment of a quantum dot device havingmultiple groups of gates in a single trench on a quantum well stack, inaccordance with various embodiments.

FIGS. 50-53 illustrate various alternative stages in the manufacture ofa quantum dot device, in accordance with various embodiments.

FIG. 54 is a cross-sectional view of a quantum dot device with multipleinterconnect layers, in accordance with various embodiments.

FIG. 55 is a cross-sectional view of a quantum dot device package, inaccordance with various embodiments.

FIGS. 56A and 56B are top views of a wafer and dies that may include anyof the quantum dot devices disclosed herein.

FIG. 57 is a cross-sectional side view of a device assembly that mayinclude any of the quantum dot devices disclosed herein.

FIG. 58 is a flow diagram of an illustrative method of operating aquantum dot device, in accordance with various embodiments.

FIG. 59 is a block diagram of an example quantum computing device thatmay include any of the quantum dot devices disclosed herein, inaccordance with various embodiments.

DETAILED DESCRIPTION

Disclosed herein are quantum dot devices, as well as related computingdevices and methods. For example, in some embodiments, a quantum dotdevice may include: a base; a fin extending away from the base, whereinthe fin includes a quantum well layer; a gate above the fin; and amaterial on side faces of the fin; wherein the fin has a width betweenits side faces, and the fin is strained in the direction of the width.

The quantum dot devices disclosed herein may enable the formation ofquantum dots to serve as quantum bits (“qubits”) in a quantum computingdevice, as well as the control of these quantum dots to perform quantumlogic operations. Unlike previous approaches to quantum dot formationand manipulation, various embodiments of the quantum dot devicesdisclosed herein provide strong spatial localization of the quantum dots(and therefore good control over quantum dot interactions andmanipulation), good scalability in the number of quantum dots includedin the device, and/or design flexibility in making electricalconnections to the quantum dot devices to integrate the quantum dotdevices in larger computing devices.

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown, byway of illustration, embodiments that may be practiced. It is to beunderstood that other embodiments may be utilized, and structural orlogical changes may be made, without departing from the scope of thepresent disclosure. Therefore, the following detailed description is notto be taken in a limiting sense.

Various operations may be described as multiple discrete actions oroperations in turn in a manner that is most helpful in understanding theclaimed subject matter. However, the order of description should not beconstrued as to imply that these operations are necessarily orderdependent. In particular, these operations may not be performed in theorder of presentation. Operations described may be performed in adifferent order from the described embodiment. Various additionaloperations may be performed, and/or described operations may be omittedin additional embodiments.

For the purposes of the present disclosure, the phrase “A and/or B”means (A), (B), or (A and B). For the purposes of the presentdisclosure, the phrase “A, B, and/or C” means (A), (B), (C), (A and B),(A and C), (B and C), or (A, B, and C). The term “between,” when usedwith reference to measurement ranges, is inclusive of the ends of themeasurement ranges. As used herein, the notation “A/B/C” means (A), (B),and/or (C). For convenience, the collection of drawings of FIGS. 1A and1B may be referred to herein as “FIG. 1.”

The description uses the phrases “in an embodiment” or “in embodiments,”which may each refer to one or more of the same or differentembodiments. Furthermore, the terms “comprising,” “including,” “having,”and the like, as used with respect to embodiments of the presentdisclosure, are synonymous. The disclosure may use perspective-baseddescriptions such as “above,” “below,” “top,” “bottom,” and “side”; suchdescriptions are used to facilitate the discussion and are not intendedto restrict the application of disclosed embodiments. The accompanyingdrawings are not necessarily drawn to scale. As used herein, a “high-kdielectric” refers to a material having a higher dielectric constantthan silicon oxide. As used herein, a “magnet line” refers to a magneticfield-generating structure to influence (e.g., change, reset, scramble,or set) the spin states of quantum dots. One example of a magnet line,as discussed herein, is a conductive pathway that is proximate to anarea of quantum dot formation and selectively conductive of a currentpulse that generates a magnetic field to influence a spin state of aquantum dot in the area.

FIGS. 1-3 are cross-sectional views of a quantum dot device 100, inaccordance with various embodiments. In particular, FIG. 2 illustratesthe quantum dot device 100 taken along the section A-A of FIG. 1 (whileFIG. 1 illustrates the quantum dot device 100 taken along the sectionC-C of FIG. 2), and FIG. 3 illustrates the quantum dot device 100 takenalong the section B-B of FIG. 1 with a number of components not shown tomore readily illustrate how the gates 106/108 and the magnet line 121may be patterned (while FIG. 1 illustrates a quantum dot device 100taken along the section D-D of FIG. 3). FIG. 1B is a detail view of aportion of FIG. 1A, showing the fin liner 131 contacting the side facesof the quantum well layer 152, and the fill material 128 as proximate tothe side faces of the quantum well layer 152. Although FIG. 1 indicatesthat the cross-section illustrated in FIG. 2 is taken through the fin104-1, an analogous cross-section taken through the fin 104-2 may beidentical, and thus the discussion of FIG. 2 refers generally to the“fin 104.”

The quantum dot device 100 may include a base 102 and multiple fins 104extending away from the base 102. The base 102 and the fins 104 mayinclude a substrate and a quantum well stack (not shown in FIGS. 1-3,but discussed below with reference to the substrate 144 and the quantumwell stack 146), distributed in any of a number of ways between the base102 and the fins 104. The base 102 may include at least some of thesubstrate, and the fins 104 may each include a quantum well layer of thequantum well stack (discussed below with reference to the quantum welllayer 152). Examples of base/fin arrangements are discussed below withreference to the base fin arrangements 158 of FIGS. 40-46.

Although only two fins, 104-1 and 104-2, are shown in FIGS. 1-3, this issimply for ease of illustration, and more than two fins 104 may beincluded in the quantum dot device 100. In some embodiments, the totalnumber of fins 104 included in the quantum dot device 100 is an evennumber, with the fins 104 organized into pairs including one active fin104 and one read fin 104, as discussed in detail below. When the quantumdot device 100 includes more than two fins 104, the fins 104 may bearranged in pairs in a line (e.g., 2N fins total may be arranged in a1×2N line, or a 2×N line) or in pairs in a larger array (e.g., 2N finstotal may be arranged as a 4×N/2 array, a 6×N/3 array, etc.). Thediscussion herein will largely focus on a single pair of fins 104 forease of illustration, but all the teachings of the present disclosureapply to quantum dot devices 100 with more fins 104.

As noted above, each of the fins 104 may include a quantum well layer(not shown in FIGS. 1-3, but discussed below with reference to thequantum well layer 152). The quantum well layer included in the fins 104may be arranged normal to the z-direction, and may provide a layer inwhich a two-dimensional electron gas (2 DEG) may form to enable thegeneration of a quantum dot during operation of the quantum dot device100, as discussed in further detail below. The quantum well layer itselfmay provide a geometric constraint on the z-location of quantum dots inthe fins 104, and the limited extent of the fins 104 (and therefore thequantum well layer) in the y-direction may provide a geometricconstraint on the y-location of quantum dots in the fins 104. To controlthe x-location of quantum dots in the fins 104, voltages may be appliedto gates disposed on the fins 104 to adjust the energy profile along thefins 104 in the x-direction and thereby constrain the x-location ofquantum dots within quantum wells (discussed in detail below withreference to the gates 106/108). The dimensions of the fins 104 may takeany suitable values. For example, in some embodiments, the fins 104 mayeach have a width 162 between 10 nanometers and 30 nanometers. In someembodiments, the fins 104 may each have a vertical dimension 164 between200 nanometers and 400 nanometers (e.g., between 250 nanometers and 350nanometers, or equal to 300 nanometers).

The fins 104 may be arranged in parallel, as illustrated in FIGS. 1 and3. In some embodiments, the fins 104 may be spaced apart by a distance160 between 100 nanometers and 250 nanometers. An electricallyinsulating fill material 128 may be disposed between the fins 104. Insome embodiments, the fill material 128 may induce strain in the fins104, improving performance of the quantum dot device 100. In particular,the fill material 128 may be laterally proximate to the quantum welllayer 152 (as shown in FIG. 1B, and as discussed further below), and mayinduce strain in the quantum well layer 152. In particular, tensilestrain may improve electron mobility (and thus may be useful for quantumdot devices 100 in which electrons are the carriers of interest, asdiscussed above) and compressive strain may improve hole mobility (andthus may be useful for quantum dot devices 100 in which holes are thecarriers of interest, as discussed above). Strain may also increasevalley splitting, which may be advantageous for the operation of aquantum dot device 100. In embodiments in which the fin liner 131 is notpresent, the fill material 128 may contact the side faces of the quantumwell layer 152. The fill material 128 may include any dielectricmaterial that can induce a desired strain in the fins 104. In someembodiments, the fill material 128 may be a nitride (e.g., siliconnitride or another nitride). In some embodiments, the fill material 128may include germanium, carbon, or phosphorous. The strain induced in thefin 104 by the fill material 128 may be controlled by selecting thematerial composition of the fill material 128 and the process conditionsunder which the fill material 128 is formed (e.g., temperature,additives, etc.). Example deposition techniques that may be used to formthe fill material 128 may include chemical vapor deposition (CVD) or aspin-on technique. In some embodiments of the quantum dot devices 100disclosed herein, the fill material 128 may not contribute to the straininduced in the fins 104. In some such embodiments, the fill material 128may include silicon oxide, silicon nitride, silicon carbide, siliconoxynitride, or silicon oxycarbide.

As illustrated in FIG. 1, in some embodiments, a fin liner 131 may bedisposed on side faces of the fins 104. The fin liner 131 may be adielectric material that may induce strain in the fins 104, improvingperformance of the quantum dot device 100. In particular, the fin liner131 may contact the side faces of the quantum well layer 152 in aquantum well stack 146 (as discussed further below), inducing strain inthe quantum well layer 152 to improve performance of the quantum dotdevice 100, as discussed above.

In embodiments in which the fin liner 131 is present, the fin liner 131may have a different material structure than the fill material 128. Asused herein, two materials may have a same “material structure” whentheir chemical composition and internal strain are approximately thesame; two materials may have a different “material structure” when theirchemical composition and/or their internal strain differ. As usedherein, a “relaxed” material may be a material that is substantiallyfree from compressive or tensile strain, while a “strained” material maybe a material exhibiting compressive or tensile strain. In someembodiments, the fin liner 131 may be an oxide material (e.g., siliconoxide) or a nitride material (e.g., silicon nitride). In someembodiments, the fin liner 131 may include carbon or phosphorous. Thestrain induced in the fin 104 by the fin liner 131 may be controlled byselecting the material composition of the fin liner 131 and the processconditions under which the fin liner 131 is formed (e.g., temperature,additives, etc.). Example deposition techniques that may be used to formthe fin liner 131 may include thermal CVD or atomic layer deposition(ALD). The fin liner 131 may have any suitable dimensions. For example,in some embodiments, a thickness 175 of the fin liner 131 may be between1 nanometer and 10 nanometers (e.g., between 2 nanometers and 3nanometers). Increasing the thickness 175 of a fin liner 131 mayincrease the amount of strain that may be induced in the fins 104, butthe thickness 175 of the fin liner 131 may be constrained by a desireddistance 160 between the fins 104. FIG. 1 illustrates an embodiment inwhich the fin liner 131 has a substantially uniform thickness on theside faces of the fins 104, but this need not be the case. In someembodiments, no fin liner 131 may be present in a quantum dot device100.

In some embodiments, the fill material 128 and/or the fin liner 131 mayinduce strain in the fins 104 such that the greater strain is induced inthe quantum well layer 152 than in other layers of a quantum well stack146. For example, the strain profile of a fin 104 may have the maximumstrain at the top surfaces of the fins 104; this may be particularlyadvantageous when the quantum well stack 146 has the quantum well layer152 at the top (e.g., as illustrated in FIG. 37). In some embodiments,the strain induced in the fins 104 by the fill material 128 and/or thefin liner 131 may be greatest in the y-direction (corresponding to thedirection of the width 162 of the fins 104), and less in the z-directionor the x-direction.

In the embodiment of FIG. 1, the fin liner 131 is shown as disposed“vertically” on the side faces of the fins 104 and “laterally” on thebase 102 between and outside of the fins 104. In other embodiments, thefin liner 131 may not extend laterally over the base 102, as discussedbelow with reference to FIG. 47.

Multiple gates may be disposed on each of the fins 104. In theembodiment illustrated in FIG. 2, three gates 106 and two gates 108 areshown as distributed on the top of the fin 104. This particular numberof gates is simply illustrative, and any suitable number of gates may beused. Additionally, as discussed below with reference to FIG. 48,multiple groups of gates (like the gates illustrated in FIG. 2) may bedisposed on the fin 104.

As shown in FIG. 2, the gate 108-1 may be disposed between the gates106-1 and 106-2, and the gate 108-2 may be disposed between the gates106-2 and 106-3. Each of the gates 106/108 may include a gate dielectric114; in the embodiment illustrated in FIG. 2, the gate dielectric 114for all of the gates 106/108 is provided by a common layer of gatedielectric material. In other embodiments, the gate dielectric 114 foreach of the gates 106/108 may be provided by separate portions of gatedielectric 114 (e.g., as discussed below with reference to FIGS. 50-53).In some embodiments, the gate dielectric 114 may be a multilayer gatedielectric (e.g., with multiple materials used to improve the interfacebetween the fin 104 and the corresponding gate metal). The gatedielectric 114 may be, for example, silicon oxide, aluminum oxide, or ahigh-k dielectric, such as hafnium oxide. More generally, the gatedielectric 114 may include elements such as hafnium, silicon, oxygen,titanium, tantalum, lanthanum, aluminum, zirconium, barium, strontium,yttrium, lead, scandium, niobium, and zinc. Examples of materials thatmay be used in the gate dielectric 114 may include, but are not limitedto, hafnium oxide, hafnium silicon oxide, lanthanum oxide, lanthanumaluminum oxide, zirconium oxide, zirconium silicon oxide, tantalumoxide, titanium oxide, barium strontium titanium oxide, barium titaniumoxide, strontium titanium oxide, yttrium oxide, aluminum oxide, tantalumoxide, tantalum silicon oxide, lead scandium tantalum oxide, and leadzinc niobate. In some embodiments, an annealing process may be carriedout on the gate dielectric 114 to improve the quality of the gatedielectric 114.

Each of the gates 106 may include a gate metal 110 and a hardmask 116.The hardmask 116 may be formed of silicon nitride, silicon carbide, oranother suitable material. The gate metal 110 may be disposed betweenthe hardmask 116 and the gate dielectric 114, and the gate dielectric114 may be disposed between the gate metal 110 and the fin 104. Only oneportion of the hardmask 116 is labeled in FIG. 2 for ease ofillustration. In some embodiments, the gate metal 110 may be asuperconductor, such as aluminum, titanium nitride (e.g., deposited viaALD), or niobium titanium nitride. In some embodiments, the hardmask 116may not be present in the quantum dot device 100 (e.g., a hardmask likethe hardmask 116 may be removed during processing, as discussed below).The sides of the gate metal 110 may be substantially parallel, as shownin FIG. 2, and insulating spacers 134 may be disposed on the sides ofthe gate metal 110 and the hardmask 116. As illustrated in FIG. 2, thespacers 134 may be thicker closer to the fin 104 and thinner fartheraway from the fin 104. In some embodiments, the spacers 134 may have aconvex shape. The spacers 134 may be formed of any suitable material,such as a carbon-doped oxide, silicon nitride, silicon oxide, or othercarbides or nitrides (e.g., silicon carbide, silicon nitride doped withcarbon, and silicon oxynitride). The gate metal 110 may be any suitablemetal, such as titanium nitride.

Each of the gates 108 may include a gate metal 112 and a hardmask 118.The hardmask 118 may be formed of silicon nitride, silicon carbide, oranother suitable material. The gate metal 112 may be disposed betweenthe hardmask 118 and the gate dielectric 114, and the gate dielectric114 may be disposed between the gate metal 112 and the fin 104. In theembodiment illustrated in FIG. 2, the hardmask 118 may extend over thehardmask 116 (and over the gate metal 110 of the gates 106), while inother embodiments, the hardmask 118 may not extend over the gate metal110 (e.g., as discussed below with reference to FIG. 45). In someembodiments, the hardmask 118 may not be present in the quantum dotdevice 100 (e.g., a hardmask like the hardmask 118 may be removed duringprocessing, as discussed below).

In some embodiments, the gate metal 112 and the gate metal 110 may havethe same material structure; in other embodiments, the gate metal 112may have a different material structure from the gate metal 110. Inparticular, in some embodiments, the material structures of the gatemetal 110 and 112 may be different and may be selected so as to inducestrain in the underlying material layers (including the quantum welllayer 152).

The strain induced in the underlying material layers by the gate metal110/112 may not be uniform through these underlying material layers, butmay vary along the material layers depending upon the relative locationbelow the gate metal 110/112. For example, the region of a quantum welllayer 152 below the gate metal 110 may be tensilely strained, while theregion below the gate metal 112 may be compressively strained (or viceversa). In some embodiments, the region of a quantum well layer 152below the gate metal 110 may be tensilely (compressively) strained, andthe region below the gate metal 112 may be tensilely (compressively)strained as well, but by a different amount. The gate metals 110 and 112may be selected to achieve a particular differential strain landscape inthe underlying material layers (e.g., in the quantum well layer 152)that may improve the electric field control of the potential energies inthese material layers (e.g., the “barrier” and “plunger” potentials, asdiscussed below).

In some embodiments, the gate metal 110 and or the gate metal 112 itselfmay be strained (e.g., with strain induced during deposition, as knownin the art). In other embodiments, the differential strain induced inthe quantum well layer 152 may be a function of the interaction betweenthe gate metals 110/112 and the adjacent materials (e.g., the gatedielectric 114, a barrier layer 156 (discussed below), etc.).

Differential strain may be induced in the quantum well layer 152 by thegate metal 110/112 in a number of ways. For example, differential strainmay be induced in the quantum well layer 152 when the gate metal 110 isformed of different metal than the gate metal 112. For example, in someembodiments, the gate metal 110 may be a superconductor while the gatemetal 112 is a non-superconductor (or vice versa). In some embodiments,the gate metal 110 may be titanium nitride while the gate metal 112 is ametal different than titanium nitride (e.g., aluminum or niobiumtitanium nitride) (or vice versa). In some embodiments, the gate metal110 and the gate metal 112 may be different non-magnetic metals.

Even when the gate metal 110 and the gate metal 112 include the samemetal, differential strain may be induced in the quantum well layer 152(and other intervening material layers) when the gate metal 110 and thegate metal 112 are deposited under different conditions (e.g.,precursors, time, temperature, pressure, deposition technique, etc.).For example, the gate metal 110 and the gate metal 112 may be depositedusing the same technique (e.g., ALD, electroless deposition,electroplating, or sputtering), but the parameters and/or materials ofthese deposition processes may be different, resulting in differentstructures of the gate metals 110/112 and therefore differential strainin the underlying material layers. In some embodiments, the thin filmdeposition of the gate metals 110/112 may induce strain in theunderlying quantum well layer 152.

Although various ones of the accompanying figures illustrate“alternating” gate metals 110 and 112, a quantum dot device may includemore than two different gate metals that have different materialstructures, and these different gate metals may be arranged in anydesired manner to achieve a desired strain landscape in the underlyingmaterial layers. For example, in some embodiments, three or more gatemetals with different material structures may be used in place of thegate metals 110/112 to achieve a desired strain landscape in a quantumwell layer 152.

The gate 108-1 may extend between the proximate spacers 134 on the sidesof the gate 106-1 and the gate 106-2, as shown in FIG. 2. In someembodiments, the gate metal 112 of the gate 108-1 may extend between thespacers 134 on the sides of the gate 106-1 and the gate 106-2. Thus, thegate metal 112 of the gate 108-1 may have a shape that is substantiallycomplementary to the shape of the spacers 134, as shown. Similarly, thegate 108-2 may extend between the proximate spacers 134 on the sides ofthe gate 106-2 and the gate 106-3. In some embodiments in which the gatedielectric 114 is not a layer shared commonly between the gates 108 and106, but instead is separately deposited on the fin 104 between thespacers 134 (e.g., as discussed below with reference to FIGS. 50-53),the gate dielectric 114 may extend at least partially up the sides ofthe spacers 134, and the gate metal 112 may extend between the portionsof gate dielectric 114 on the spacers 134. The gate metal 112, like thegate metal 110, may be any suitable metal, such as titanium nitride.

The dimensions of the gates 106/108 may take any suitable values. Forexample, in some embodiments, the z-height 166 of the gate metal 110 maybe between 40 nanometers and 75 nanometers (e.g., approximately 50nanometers); the z-height of the gate metal 112 may be in the samerange. In embodiments like the ones illustrated in FIG. 2, the z-heightof the gate metal 112 may be greater than the z-height of the gate metal110. In some embodiments, the length 168 of the gate metal 110 (i.e., inthe x-direction) may be between 20 nanometers and 40 nanometers (e.g.,30 nanometers). In some embodiments, the distance 170 between adjacentones of the gates 106 (e.g., as measured from the gate metal 110 of onegate 106 to the gate metal 110 of an adjacent gate 106 in thex-direction, as illustrated in FIG. 2) may be between 40 nanometers and60 nanometers (e.g., 50 nanometers). In some embodiments, the thickness172 of the spacers 134 may be between 1 nanometer and 10 nanometers(e.g., between 3 nanometers and 5 nanometers, between 4 nanometers and 6nanometers, or between 4 nanometers and 7 nanometers). The length of thegate metal 112 (i.e., in the x-direction) may depend on the dimensionsof the gates 106 and the spacers 134, as illustrated in FIG. 2. Asindicated in FIG. 1, the gates 106/108 on one fin 104 may extend overthe fill material 128 beyond their respective fins 104 and towards theother fin 104, but may be isolated from their counterpart gates by theintervening insulating material 130 and spacers 134.

Although all of the gates 106 are illustrated in the accompanyingdrawings as having the same length 168 of the gate metal 110, in someembodiments, the “outermost” gates 106 (e.g., the gates 106-1 and 106-3of the embodiment illustrated in FIG. 2) may have a greater length 168than the “inner” gates 106 (e.g., the gate 106-2 in the embodimentillustrated in FIG. 2). Such longer “outside” gates 106 may providespatial separation between the doped regions 140 and the areas under thegates 108 and the inner gates 106 in which quantum dots 142 may form,and thus may reduce the perturbations to the potential energy landscapeunder the gates 108 and the inner gates 106 caused by the doped regions140.

As shown in FIG. 2, the gates 106 and 108 may be alternatingly arrangedalong the fin 104 in the x-direction. During operation of the quantumdot device 100, voltages may be applied to the gates 106/108 to adjustthe potential energy in the quantum well layer (not shown) in the fin104 to create quantum wells of varying depths in which quantum dots 142may form. Only one quantum dot 142 is labeled with a reference numeralin FIGS. 2 and 3 for ease of illustration, but five are indicated asdotted circles in each fin 104. The location of the quantum dots 142 inFIG. 2 is not intended to indicate a particular geometric positioning ofthe quantum dots 142. The spacers 134 may themselves provide “passive”barriers between quantum wells under the gates 106/108 in the quantumwell layer, and the voltages applied to different ones of the gates106/108 may adjust the potential energy under the gates 106/108 in thequantum well layer; decreasing the potential energy may form quantumwells, while increasing the potential energy may form quantum barriers.

The fins 104 may include doped regions 140 that may serve as a reservoirof charge carriers for the quantum dot device 100. For example, ann-type doped region 140 may supply electrons for electron-type quantumdots 142, and a p-type doped region 140 may supply holes for hole-typequantum dots 142. In some embodiments, an interface material 141 may bedisposed at a surface of a doped region 140, as shown. The interfacematerial 141 may facilitate electrical coupling between a conductivecontact (e.g., a conductive via 136, as discussed below) and the dopedregion 140. The interface material 141 may be any suitablemetal-semiconductor ohmic contact material; for example, in embodimentsin which the doped region 140 includes silicon, the interface material141 may include nickel silicide, aluminum silicide, titanium silicide,molybdenum silicide, cobalt silicide, tungsten silicide, or platinumsilicide (e.g., as discussed below with reference to FIGS. 22-23). Insome embodiments, the interface material 141 may be a non-silicidecompound, such as titanium nitride. In some embodiments, the interfacematerial 141 may be a metal (e.g., aluminum, tungsten, or indium).

The quantum dot devices 100 disclosed herein may be used to formelectron-type or hole-type quantum dots 142. Note that the polarity ofthe voltages applied to the gates 106/108 to form quantum wells/barriersdepend on the charge carriers used in the quantum dot device 100. Inembodiments in which the charge carriers are electrons (and thus thequantum dots 142 are electron-type quantum dots), amply negativevoltages applied to a gate 106/108 may increase the potential barrierunder the gate 106/108, and amply positive voltages applied to a gate106/108 may decrease the potential barrier under the gate 106/108(thereby forming a potential well in which an electron-type quantum dot142 may form). In embodiments in which the charge carriers are holes(and thus the quantum dots 142 are hole-type quantum dots), amplypositive voltages applied to a gate 106/108 may increase the potentialbarrier under the gate 106/108, and amply negative voltages applied to agate 106 and 108 may decrease the potential barrier under the gate106/108 (thereby forming a potential well in which a hole-type quantumdot 142 may form). The quantum dot devices 100 disclosed herein may beused to form electron-type or hole-type quantum dots.

Voltages may be applied to each of the gates 106 and 108 separately toadjust the potential energy in the quantum well layer under the gates106 and 108, and thereby control the formation of quantum dots 142 undereach of the gates 106 and 108. Additionally, the relative potentialenergy profiles under different ones of the gates 106 and 108 allow thequantum dot device 100 to tune the potential interaction between quantumdots 142 under adjacent gates. For example, if two adjacent quantum dots142 (e.g., one quantum dot 142 under a gate 106 and another quantum dot142 under a gate 108) are separated by only a short potential barrier,the two quantum dots 142 may interact more strongly than if they wereseparated by a taller potential barrier. Since the depth of thepotential wells/height of the potential barriers under each gate 106/108may be adjusted by adjusting the voltages on the respective gates106/108, the differences in potential between adjacent gates 106/108 maybe adjusted, and thus the interaction tuned.

In some applications, the gates 108 may be used as plunger gates toenable the formation of quantum dots 142 under the gates 108, while thegates 106 may be used as barrier gates to adjust the potential barrierbetween quantum dots 142 formed under adjacent gates 108. In otherapplications, the gates 108 may be used as barrier gates, while thegates 106 are used as plunger gates. In other applications, quantum dots142 may be formed under all of the gates 106 and 108, or under anydesired subset of the gates 106 and 108.

Conductive vias and lines may make contact with the gates 106/108, andto the doped regions 140, to enable electrical connection to the gates106/108 and the doped regions 140 to be made in desired locations. Asshown in FIGS. 1-3, the gates 106 may extend away from the fins 104, andconductive vias 120 may contact the gates 106 (and are drawn in dashedlines in FIG. 2 to indicate their location behind the plane of thedrawing). The conductive vias 120 may extend through the hardmask 116and the hardmask 118 to contact the gate metal 110 of the gates 106. Thegates 108 may extend away from the fins 104, and conductive vias 122 maycontact the gates 108 (also drawn in dashed lines in FIG. 2 to indicatetheir location behind the plane of the drawing). The conductive vias 122may extend through the hardmask 118 to contact the gate metal 112 of thegates 108. Conductive vias 136 may contact the interface material 141and may thereby make electrical contact with the doped regions 140. Thequantum dot device 100 may include further conductive vias and/or lines(not shown) to make electrical contact to the gates 106/108 and/or thedoped regions 140, as desired. The conductive vias and lines included ina quantum dot device 100 may include any suitable materials, such ascopper, tungsten (deposited, e.g., by CVD), or a superconductor (e.g.,aluminum, tin, titanium nitride, niobium titanium nitride, tantalum,niobium, or other niobium compounds such as niobium tin and niobiumgermanium).

During operation, a bias voltage may be applied to the doped regions 140(e.g., via the conductive vias 136 and the interface material 141) tocause current to flow through the doped regions 140. When the dopedregions 140 are doped with an n-type material, this voltage may bepositive; when the doped regions 140 are doped with a p-type material,this voltage may be negative. The magnitude of this bias voltage maytake any suitable value (e.g., between 0.25 volts and 2 volts).

The quantum dot device 100 may include one or more magnet lines 121. Forexample, a single magnet line 121 is illustrated in FIGS. 1-3 proximateto the fin 104-1. The magnet line 121 may be formed of a conductivematerial, and may be used to conduct current pulses that generatemagnetic fields to influence the spin states of one or more of thequantum dots 142 that may form in the fins 104. In some embodiments, themagnet line 121 may conduct a pulse to reset (or “scramble”) nuclearand/or quantum dot spins. In some embodiments, the magnet line 121 mayconduct a pulse to initialize an electron in a quantum dot in aparticular spin state. In some embodiments, the magnet line 121 mayconduct current to provide a continuous, oscillating magnetic field towhich the spin of a qubit may couple. The magnet line 121 may provideany suitable combination of these embodiments, or any other appropriatefunctionality.

In some embodiments, the magnet line 121 may be formed of copper. Insome embodiments, the magnet line 121 may be formed of a superconductor,such as aluminum. The magnet line 121 illustrated in FIGS. 1-3 isnon-coplanar with the fins 104, and is also non-coplanar with the gates106/108. In some embodiments, the magnet line 121 may be spaced apartfrom the gates 106/108 by a distance 167. The distance 167 may take anysuitable value (e.g., based on the desired strength of magnetic fieldinteraction with the quantum dots 142); in some embodiments, thedistance 167 may be between 25 nanometers and 1 micron (e.g., between 50nanometers and 200 nanometers).

In some embodiments, the magnet line 121 may be formed of a magneticmaterial. For example, a magnetic material (such as cobalt) may bedeposited in a trench in the insulating material 130 to provide apermanent magnetic field in the quantum dot device 100.

The magnet line 121 may have any suitable dimensions. For example, themagnet line 121 may have a thickness 169 between 25 nanometers and 100nanometers. The magnet line 121 may have a width 171 between 25nanometers and 100 nanometers. In some embodiments, the width 171 andthickness 169 of a magnet line 121 may be equal to the width andthickness, respectively, of other conductive lines in the quantum dotdevice 100 (not shown) used to provide electrical interconnects, asknown in the art. The magnet line 121 may have a length 173 that maydepend on the number and dimensions of the gates 106/108 that are toform quantum dots 142 with which the magnet line 121 is to interact. Themagnet line 121 illustrated in FIGS. 1-3 (and the magnet lines 121illustrated in FIGS. 34-36 below) are substantially linear, but thisneed not be the case; the magnet lines 121 disclosed herein may take anysuitable shape. Conductive vias 123 may contact the magnet line 121.

The conductive vias 120, 122, 136, and 123 may be electrically isolatedfrom each other by an insulating material 130. The insulating material130 may be any suitable material, such as an interlayer dielectric(ILD). Examples of the insulating material 130 may include siliconoxide, silicon nitride, aluminum oxide, carbon-doped oxide, and/orsilicon oxynitride. As known in the art of integrated circuitmanufacturing, conductive vias and lines may be formed in an iterativeprocess in which layers of structures are formed on top of each other.In some embodiments, the conductive vias 120/122/136/123 may have awidth that is 20 nanometers or greater at their widest point (e.g., 30nanometers), and a pitch of 80 nanometers or greater (e.g., 100nanometers). In some embodiments, conductive lines (not shown) includedin the quantum dot device 100 may have a width that is 100 nanometers orgreater, and a pitch of 100 nanometers or greater. The particulararrangement of conductive vias shown in FIGS. 1-3 is simplyillustrative, and any electrical routing arrangement may be implemented.

As discussed above, the structure of the fin 104-1 may be the same asthe structure of the fin 104-2; similarly, the construction of gates106/108 on the fin 104-1 may be the same as the construction of gates106/108 on the fin 104-2. The gates 106/108 on the fin 104-1 may bemirrored by corresponding gates 106/108 on the parallel fin 104-2, andthe insulating material 130 may separate the gates 106/108 on thedifferent fins 104-1 and 104-2. In particular, quantum dots 142 formedin the fin 104-1 (under the gates 106/108) may have counterpart quantumdots 142 in the fin 104-2 (under the corresponding gates 106/108). Insome embodiments, the quantum dots 142 in the fin 104-1 may be used as“active” quantum dots in the sense that these quantum dots 142 act asqubits and are controlled (e.g., by voltages applied to the gates106/108 of the fin 104-1) to perform quantum computations. The quantumdots 142 in the fin 104-2 may be used as “read” quantum dots in thesense that these quantum dots 142 may sense the quantum state of thequantum dots 142 in the fin 104-1 by detecting the electric fieldgenerated by the charge in the quantum dots 142 in the fin 104-1, andmay convert the quantum state of the quantum dots 142 in the fin 104-1into electrical signals that may be detected by the gates 106/108 on thefin 104-2. Each quantum dot 142 in the fin 104-1 may be read by itscorresponding quantum dot 142 in the fin 104-2. Thus, the quantum dotdevice 100 enables both quantum computation and the ability to read theresults of a quantum computation.

The quantum dot devices 100 disclosed herein may be manufactured usingany suitable techniques. FIGS. 4-33 illustrate various example stages inthe manufacture of the quantum dot device 100 of FIGS. 1-3, inaccordance with various embodiments. Although the particularmanufacturing operations discussed below with reference to FIGS. 4-33are illustrated as manufacturing a particular embodiment of the quantumdot device 100, these operations may be applied to manufacture manydifferent embodiments of the quantum dot device 100, as discussedherein. Any of the elements discussed below with reference to FIGS. 4-33may take the form of any of the embodiments of those elements discussedabove (or otherwise disclosed herein).

FIG. 4 illustrates a cross-sectional view of an assembly 200 including asubstrate 144. The substrate 144 may include any suitable semiconductormaterial or materials. In some embodiments, the substrate 144 mayinclude a semiconductor material. For example, the substrate 144 mayinclude silicon (e.g., may be formed from a silicon wafer). Variousembodiments of the substrate 144 are discussed below with reference toFIGS. 37-39.

FIG. 5 illustrates a cross-sectional view of an assembly 202 subsequentto providing a quantum well stack 146 on the substrate 144 of theassembly 200 (FIG. 4). The quantum well stack 146 may include a quantumwell layer (not shown) in which a 2DEG may form during operation of thequantum dot device 100. Various embodiments of the quantum well stack146 are discussed below with reference to FIGS. 37-39.

FIG. 6 illustrates a cross-sectional view of an assembly 204 subsequentto forming fins 104 in the assembly 202 (FIG. 5). The fins 104 mayextend from a base 102, and may be formed in the assembly 202 bypatterning and then etching the assembly 202, as known in the art. Forexample, a combination of dry and wet etch chemistry may be used to formthe fins 104, and the appropriate chemistry may depend on the materialsincluded in the assembly 202, as known in the art. At least some of thesubstrate 144 may be included in the base 102, and at least some of thequantum well stack 146 may be included in the fins 104. In particular,the quantum well layer (not shown) of the quantum well stack 146 may beincluded in the fins 104. Example arrangements in which the quantum wellstack 146 and the substrate 144 are differently included in the base 102and the fins 104 are discussed below with reference to FIGS. 40-46.

FIG. 7 illustrates a cross-sectional view of an assembly 206 subsequentto providing a fin liner 131 on the fins 104 of the assembly 204 (FIG.6), and then forming a fill material 128. In some embodiments, the finliner 131 may be conformally deposited over the assembly 204, and thematerial composition and deposition conditions of the fin liner 131 maybe selected so as to induce a desired strain in the fins 104, asdiscussed above. Further, in some embodiments, the fill material 128 maybe deposited so as to induce strain in the fins 104, as discussed above.In some embodiments, the fin liner 131 may not be present.

FIG. 8 illustrates a cross-sectional view of an assembly 208 subsequentto planarizing the assembly 206 (FIG. 7) to remove the fin liner 131 andthe fill material 128 above the fins 104. In some embodiments, theassembly 206 may be planarized using a chemical mechanical polishing(CMP) technique.

FIG. 9 is a perspective view of at least a portion of the assembly 208,showing the fins 104 extending from the base 102 and separated by thefin liner 131 and the fill material 128. The cross-sectional views ofFIGS. 4-8 are taken parallel to the plane of the page of the perspectiveview of FIG. 9. FIG. 10 is another cross-sectional view of the assembly208, taken along the dashed line along the fin 104-1 in FIG. 9. Thecross-sectional views illustrated in FIGS. 11-24, 26, 28, 30, and 32 aretaken along the same cross-section as FIG. 10. The cross-sectional viewsillustrated in FIGS. 25, 27, 29, 31, and 33 are taken along the samecross-section as FIG. 8.

FIG. 11 is a cross-sectional view of an assembly 210 subsequent toforming a gate stack 174 on the fins 104 of the assembly 208 (FIGS.8-10). The gate stack 174 may include the gate dielectric 114, the gatemetal 110, and a hardmask 116. The hardmask 116 may be formed of anelectrically insulating material, such as silicon nitride orcarbon-doped nitride.

FIG. 12 is a cross-sectional view of an assembly 212 subsequent topatterning the hardmask 116 of the assembly 210 (FIG. 11). The patternapplied to the hardmask 116 may correspond to the locations for thegates 106, as discussed below. The hardmask 116 may be patterned byapplying a resist, patterning the resist using lithography, and thenetching the hardmask (using dry etching or any appropriate technique).

FIG. 13 is a cross-sectional view of an assembly 214 subsequent toetching the assembly 212 (FIG. 12) to remove the gate metal 110 that isnot protected by the patterned hardmask 116 to form the gates 106. Insome embodiments, as illustrated in FIG. 13, the gate dielectric 114 mayremain after the gate metal 110 is etched away; in other embodiments,the gate dielectric 114 may also be etched during the etching of thegate metal 110. Examples of such embodiments are discussed below withreference to FIGS. 50-53.

FIG. 14 is a cross-sectional view of an assembly 216 subsequent toproviding spacer material 132 on the assembly 214 (FIG. 13). The spacermaterial 132 may include any of the materials discussed above withreference to the spacers 134, for example, and may be deposited usingany suitable technique. For example, the spacer material 132 may be anitride material (e.g., silicon nitride) deposited by sputtering.

FIG. 15 is a cross-sectional view of an assembly 218 subsequent toetching the spacer material 132 of the assembly 216 (FIG. 14), leavingspacers 134 formed of the spacer material 132 on the sides of the gates106 (e.g., on the sides of the hardmask 116 and the gate metal 110). Theetching of the spacer material 132 may be an anisotropic etch, etchingthe spacer material 132 “downward” to remove the spacer material 132 ontop of the gates 106 and in some of the area between the gates 106,while leaving the spacers 134 on the sides of the gates 106. In someembodiments, the anisotropic etch may be a dry etch.

FIG. 16 is a cross-sectional view of an assembly 220 subsequent toproviding the gate metal 112 on the assembly 218 (FIG. 15). The gatemetal 112 may fill the areas between adjacent ones of the gates 106, andmay extend over the tops of the gates 106.

FIG. 17 is a cross-sectional view of an assembly 222 subsequent toplanarizing the assembly 220 (FIG. 16) to remove the gate metal 112above the gates 106. In some embodiments, the assembly 220 may beplanarized using a CMP technique. Some of the remaining gate metal 112may fill the areas between adjacent ones of the gates 106, while otherportions 150 of the remaining gate metal 112 may be located “outside” ofthe gates 106.

FIG. 18 is a cross-sectional view of an assembly 224 subsequent toproviding a hardmask 118 on the planarized surface of the assembly 222(FIG. 17). The hardmask 118 may be formed of any of the materialsdiscussed above with reference to the hardmask 116, for example.

FIG. 19 is a cross-sectional view of an assembly 226 subsequent topatterning the hardmask 118 of the assembly 224 (FIG. 18). The patternapplied to the hardmask 118 may extend over the hardmask 116, over thegate metal 110 of the gates 106, and over the locations for the gates108 (as illustrated in FIG. 2). The hardmask 118 may be non-coplanarwith the hardmask 116, as illustrated in FIG. 19. The hardmask 118illustrated in FIG. 19 may thus be a common, continuous portion ofhardmask 118 that extends over all of the hardmask 116. The hardmask 118may be patterned using any of the techniques discussed above withreference to the patterning of the hardmask 116, for example.

FIG. 20 is a cross-sectional view of an assembly 228 subsequent toetching the assembly 226 (FIG. 19) to remove the portions 150 that arenot protected by the patterned hardmask 118 to form the gates 108.Portions of the hardmask 118 may remain on top of the hardmask 116, asshown. The operations performed on the assembly 226 may include removingany gate dielectric 114 that is “exposed” on the fin 104, as shown. Theexcess gate dielectric 114 may be removed using any suitable technique,such as chemical etching or silicon bombardment.

FIG. 21 is a cross-sectional view of an assembly 230 subsequent todoping the fins 104 of the assembly 228 (FIG. 20) to form doped regions140 in the portions of the fins 104 “outside” of the gates 106/108. Thetype of dopant used to form the doped regions 140 may depend on the typeof quantum dot desired, as discussed above. In some embodiments, thedoping may be performed by ion implantation. For example, when thequantum dot 142 is to be an electron-type quantum dot 142, the dopedregions 140 may be formed by ion implantation of phosphorous, arsenic,or another n-type material. When the quantum dot 142 is to be ahole-type quantum dot 142, the doped regions 140 may be formed by ionimplantation of boron or another p-type material. An annealing processthat activates the dopants and causes them to diffuse farther into thefins 104 may follow the ion implantation process. The depth of the dopedregions 140 may take any suitable value; for example, in someembodiments, the doped regions 140 may extend into the fin 104 to adepth 115 between 500 Angstroms and 1000 Angstroms.

The outer spacers 134 on the outer gates 106 may provide a dopingboundary, limiting diffusion of the dopant from the doped regions 140into the area under the gates 106/108. As shown, the doped regions 140may extend under the adjacent outer spacers 134. In some embodiments,the doped regions 140 may extend past the outer spacers 134 and underthe gate metal 110 of the outer gates 106, may extend only to theboundary between the outer spacers 134 and the adjacent gate metal 110,or may terminate under the outer spacers 134 and not reach the boundarybetween the outer spacers 134 and the adjacent gate metal 110. Thedoping concentration of the doped regions 140 may, in some embodiments,be between 10¹⁷/cm³ and 10²⁰/cm³.

FIG. 22 is a cross-sectional side view of an assembly 232 subsequent toproviding a layer of nickel or other material 143 over the assembly 230(FIG. 21). The nickel or other material 143 may be deposited on theassembly 230 using any suitable technique (e.g., a plating technique,CVD, or ALD).

FIG. 23 is a cross-sectional side view of an assembly 234 subsequent toannealing the assembly 232 (FIG. 22) to cause the material 143 tointeract with the doped regions 140 to form the interface material 141,then removing the unreacted material 143. When the doped regions 140include silicon and the material 143 includes nickel, for example, theinterface material 141 may be nickel silicide. Materials other thannickel may be deposited in the operations discussed above with referenceto FIG. 22 in order to form other interface materials 141, includingtitanium, aluminum, molybdenum, cobalt, tungsten, or platinum, forexample. More generally, the interface material 141 of the assembly 234may include any of the materials discussed herein with reference to theinterface material 141.

FIG. 24 is a cross-sectional view of an assembly 236 subsequent toproviding an insulating material 130 on the assembly 234 (FIG. 23). Theinsulating material 130 may take any of the forms discussed above. Forexample, the insulating material 130 may be a dielectric material, suchas silicon oxide. The insulating material 130 may be provided on theassembly 234 using any suitable technique, such as spin coating, CVD, orplasma-enhanced CVD (PECVD). In some embodiments, the insulatingmaterial 130 may be polished back after deposition, and before furtherprocessing. In some embodiments, the thickness 173 of the insulatingmaterial 130 provided on the assembly 236 (as measured from the hardmask118, as indicated in FIG. 24) may be between 50 nanometers and 1.2microns (e.g., between 50 nanometers and 300 nanometers). FIG. 25 isanother cross-sectional view of the assembly 236, taken along thesection C-C of FIG. 24.

FIG. 26 is a cross-sectional view of an assembly 238 subsequent toforming a trench 125 in the insulating material 130 of the assembly 236(FIGS. 24 and 25). The trench 125 may be formed using any desiredtechniques (e.g., resist patterning followed by etching), and may have adepth 127 and a width 129 that may take the form of any of theembodiments of the thickness 169 and the width 171, respectively,discussed above with reference to the magnet line 121. FIG. 27 isanother cross-sectional view of the assembly 238, taken along thesection C-C of FIG. 26. In some embodiments, the assembly 236 may beplanarized to remove the hardmasks 116 and 118, then additionalinsulating material 130 may be provided on the planarized surface beforeforming the trench 125; in such an embodiment, the hardmasks 116 and 118would not be present in the quantum dot device 100.

FIG. 28 is a cross-sectional view of an assembly 240 subsequent tofilling the trench 125 of the assembly 238 (FIGS. 26 and 27) with aconductive material to form the magnet line 121. The magnet line 121 maybe formed using any desired techniques (e.g., plating followed byplanarization, or a semi-additive process), and may take the form of anyof the embodiments disclosed herein. FIG. 29 is another cross-sectionalview of the assembly 240, taken along the section C-C of FIG. 28.

FIG. 30 is a cross-sectional view of an assembly 242 subsequent toproviding additional insulating material 130 on the assembly 240 (FIGS.28 and 29). The insulating material 130 provided on the assembly 240 maytake any of the forms of the insulating material 130 discussed above.FIG. 31 is another cross-sectional view of the assembly 242, taken alongthe section C-C of FIG. 30.

FIG. 32 is a cross-sectional view of an assembly 244 subsequent toforming, in the assembly 242 (FIGS. 30 and 31), conductive vias 120through the insulating material 130 (and the hardmasks 116 and 118) tocontact the gate metal 110 of the gates 106, conductive vias 122 throughthe insulating material 130 (and the hardmask 118) to contact the gatemetal 112 of the gates 108, conductive vias 136 through the insulatingmaterial 130 to contact the interface material 141 of the doped regions140, and conductive vias 123 through the insulating material 130 tocontact the magnet line 121. FIG. 33 is another cross-sectional view ofthe assembly 244, taken along the section C-C of FIG. 32. Furtherconductive vias and/or lines may be formed in the assembly 244 usingconventional interconnect techniques, if desired. The resulting assembly244 may take the form of the quantum dot device 100 discussed above withreference to FIGS. 1-3.

In the embodiment of the quantum dot device 100 illustrated in FIGS.1-3, the magnet line 121 is oriented parallel to the longitudinal axesof the fins 104. In other embodiments, the magnet line 121 may not beoriented parallel to the longitudinal axes of the fins 104. For example,FIGS. 34-36 are various cross-sectional views of an embodiment of aquantum dot device 100 having multiple magnet lines 121, each proximateto the fins 104 and oriented perpendicular to the longitudinal axes ofthe fins 104. Other than orientation, the magnet lines 121 of theembodiment of FIGS. 34-36 may take the form of any of the embodiments ofthe magnet line 121 discussed above. The other elements of the quantumdot devices 100 of FIGS. 34-36 may take the form of any of thoseelements discussed herein. The manufacturing operations discussed abovewith reference to FIGS. 4-33 may be used to manufacture the quantum dotdevice 100 of FIGS. 34-36.

Although a single magnet line 121 is illustrated in FIGS. 1-3, multiplemagnet lines 121 may be included in that embodiment of the quantum dotdevice 100 (e.g., multiple magnet lines 121 parallel to the longitudinalaxes of the fins 104). For example, the quantum dot device 100 of FIGS.1-3 may include a second magnet line 121 proximate to the fin 104-2 in asymmetric manner to the magnet line 121 illustrated proximate to the fin104-1. In some embodiments, multiple magnet lines 121 may be included ina quantum dot device 100, and these magnet lines 121 may or may not beparallel to one another. For example, in some embodiments, a quantum dotdevice 100 may include two (or more) magnet lines 121 that are orientedperpendicular to each other (e.g., one or more magnet lines 121 orientedlike those illustrated in FIGS. 1-3, and one or more magnet lines 121oriented like those illustrated in FIGS. 34-36).

As discussed above, the base 102 and the fin 104 of a quantum dot device100 may be formed from a substrate 144 and a quantum well stack 146disposed on the substrate 144. The quantum well stack 146 may include aquantum well layer in which a 2DEG may form during operation of thequantum dot device 100. The quantum well stack 146 may take any of anumber of forms, several of which are discussed below with reference toFIGS. 37-39. The various layers in the quantum well stacks 146 discussedbelow may be grown on the substrate 144 (e.g., using epitaxialprocesses). Although the singular term “layer” may be used to refer tovarious components of the quantum well stack 146 of FIGS. 37-39, any ofthe layers discussed below may include multiple materials arranged inany suitable manner. Layers other than the quantum well layer 152 in aquantum well stack 146 may have higher threshold voltages for conductionthan the quantum well layer 152 so that when the quantum well layer 152are biased at their threshold voltages, the quantum well layer 152conducts and the other layers of the quantum well stack 146 do not. Thismay avoid parallel conduction in both the quantum well layer 152 and theother layers, and thus avoid compromising the strong mobility of thequantum well layer 152 with conduction in layers having inferiormobility. In some embodiments, silicon used in a quantum well stack 146(e.g., in a quantum well layer 152) may be grown from precursorsenriched with the 28Si isotope. In some embodiments, germanium used in aquantum well stack 146 (e.g., in a quantum well layer 152) may be grownfrom precursors enriched with the 70Ge, 72Ge, or 74Ge isotope. As notedabove, different regions of a quantum well layer 152 of a quantum dotdevice 100 may be relaxed or strained (e.g., depending upon thedifferential material structure of the gate metals 110 and 112 proximateto those regions of the quantum well layer 152). Further, whenadditional material layers in a quantum well stack are disposed betweenthe quantum well layer 152 and the gate metal 110/112 (e.g., a barrierlayer 156, as discussed below), different regions of those materiallayers may be relaxed or strained depending upon the differentialmaterial structure of the gate metals 110 and 112 proximate to thoseregions of the material layers.

FIG. 37 is a cross-sectional view of a quantum well stack 146 on asubstrate 144. The quantum well stack 146 may include a buffer layer 154on the substrate 144, and a quantum well layer 152 on the buffer layer154. In some embodiments of the quantum dot device 100 including thearrangement of FIG. 37, the gate dielectric 114 (not shown) may bedirectly on the quantum well layer 152. The quantum well layer 152 maybe formed of a material such that, during operation of the quantum dotdevice 100, a 2DEG may form in the quantum well layer 152 proximate tothe upper surface of the quantum well layer 152.

In some embodiments, the quantum well layer 152 of FIG. 37 may be formedof intrinsic silicon, and the gate dielectric 114 may be formed ofsilicon oxide; in such an arrangement, during use of the quantum dotdevice 100, a 2DEG may form in the intrinsic silicon at the interfacebetween the intrinsic silicon and the silicon oxide. Embodiments inwhich the quantum well layer 152 of FIG. 37 is formed of intrinsicsilicon may be particularly advantageous for electron-type quantum dotdevices 100. In some embodiments, the quantum well layer 152 of FIG. 37may be formed of intrinsic germanium, and the gate dielectric 114 may beformed of germanium oxide; in such an arrangement, during use of thequantum dot device 100, a 2DEG may form in the intrinsic germanium atthe interface between the intrinsic germanium and the germanium oxide.Such embodiments may be particularly advantageous for hole-type quantumdot devices 100. The quantum well layers 152 disclosed herein may bedifferentially strained, with its strain induced by the gate metal110/112, as discussed above.

The buffer layer 154 may be formed of the same material as the quantumwell layer 152 (e.g., silicon or germanium), and may be present to trapdefects that form in this material as it is grown on the substrate 144.In some embodiments, the buffer layer 154 may be grown under differentconditions (e.g., deposition temperature or growth rate) from thequantum well layer 152. In particular, the quantum well layer 152 may begrown under conditions that achieve fewer defects than in the bufferlayer 154.

FIG. 38 is a cross-sectional view of an arrangement including a quantumwell stack 146 that includes a buffer layer 154, a barrier layer 156-1,a quantum well layer 152, and an additional barrier layer 156-2. Thebarrier layer 156-1 (156-2) may provide a potential barrier between thequantum well layer 152 and the buffer layer 154 (gate dielectric 114,not shown). In some embodiments in which the quantum well layer 152includes silicon or germanium, the barrier layers 156 may includesilicon germanium. The germanium content of this silicon germanium maybe between 20 atomic-percent and 80 atomic-percent (e.g., between 30atomic-percent and 70 atomic-percent).

In some embodiments of the arrangement of FIG. 38, the buffer layer 154and the barrier layer 156-1 may be formed of silicon germanium. In somesuch embodiments, the silicon germanium of the buffer layer 154 may havea germanium content that varies (e.g., continuously or in a stepwisemanner) from the substrate 144 to the barrier layer 156-1; for example,the silicon germanium of the buffer layer 154 may have a germaniumcontent that varies from zero percent at the substrate to a nonzeropercent (e.g., between 30 atomic-percent and 70 atomic-percent) at thebarrier layer 156-1. The barrier layer 156-1 may in turn have agermanium content equal to the nonzero percent. In other embodiments,the buffer layer 154 may have a germanium content equal to the germaniumcontent of the barrier layer 156-1 but may be thicker than the barrierlayer 156-1 to absorb the defects that arise during growth. In someembodiments of the quantum well stack 146 of FIG. 38, the barrier layer156-2 may be omitted.

FIG. 39 is a cross-sectional view of another example quantum well stack146 on an example substrate 144. The quantum well stack 146 of FIG. 39may include an insulating layer 155 on the substrate 144, a quantum welllayer 152 on the insulating layer 155, and a barrier layer 156 on thequantum well layer 152. The presence of the insulating layer 155 mayhelp confine carriers to the quantum well layer 152, providing highvalley splitting during operation.

In some embodiments, the substrate 144 of FIG. 39 may include silicon.The insulating layer 155 may include any suitable electricallyinsulating material. For example, in some embodiments, the insulatinglayer 155 may be an oxide (e.g., silicon oxide or hafnium oxide). Thesubstrate 144, the quantum well layer 152, and/or the barrier layer 156of FIG. 39 may take the form of any of the embodiments disclosed herein.In some embodiments, the quantum well layer 152 may be formed on theinsulating layer 155 by a layer transfer technique. In some embodiments,the barrier layer 156 may be omitted from the quantum well stack 146 ofFIG. 39.

The thicknesses (i.e., z-heights) of the layers in the quantum wellstacks 146 of FIGS. 37-39 may take any suitable values. For example, insome embodiments, the thickness of the quantum well layer 152 may bebetween 5 nanometers and 15 nanometers (e.g., approximately equal to 10nanometers). In some embodiments, the thickness of a buffer layer 154may be between 0.3 microns and 4 microns (e.g., between 0.3 microns and2 microns, or approximately 0.5 microns). In some embodiments, thethickness of the barrier layers 156 may be between 0 nanometers and 300nanometers. In some embodiments, the thickness of the insulating layer155 in the quantum well stack 146 of FIG. 39 may be between 5 nanometersand 200 nanometers.

The substrate 144 and the quantum well stack 146 may be distributedbetween the base 102 and the fins 104 of the quantum dot device 100, asdiscussed above. This distribution may occur in any of a number of ways.For example, FIGS. 40-46 illustrate example base/fin arrangements 158that may be used in a quantum dot device 100, in accordance with variousembodiments.

In the base/fin arrangement 158 of FIG. 40, the quantum well stack 146may be included in the fins 104, but not in the base 102. The substrate144 may be included in the base 102, but not in the fins 104. When thebase/fin arrangement 158 of FIG. 40 is used in the manufacturingoperations discussed with reference to FIGS. 5-6, the fin etching mayetch through the quantum well stack 146, and stop when the substrate 144is reached.

In the base/fin arrangement 158 of FIG. 41, the quantum well stack 146may be included in the fins 104, as well as in a portion of the base102. A substrate 144 may be included in the base 102 as well, but not inthe fins 104. When the base/fin arrangement 158 of FIG. 41 is used inthe manufacturing operations discussed with reference to FIGS. 5-6, thefin etching may etch partially through the quantum well stack 146, andstop before the substrate 144 is reached. FIG. 42 illustrates aparticular embodiment of the base/fin arrangement 158 of FIG. 41. In theembodiment of FIG. 42, the quantum well stack 146 of FIG. 37 is used;the base 102 includes the substrate 144 and a portion of the bufferlayer 154 of the quantum well stack 146, while the fins 104 include theremainder of the quantum well stack 146.

In the base/fin arrangement 158 of FIG. 43, the quantum well stack 146may be included in the fins 104, but not the base 102. The substrate 144may be partially included in the fins 104, as well as in the base 102.When the base/fin arrangement 158 of FIG. 43 is used in themanufacturing operations discussed with reference to FIGS. 5-6, the finetching may etch through the quantum well stack 146 and into thesubstrate 144 before stopping. FIG. 44 illustrates a particularembodiment of the base/fin arrangement 158 of FIG. 43. In the embodimentof FIG. 44, the quantum well stack 146 of FIG. 39 is used; the fins 104include the quantum well stack 146 and a portion of the substrate 144,while the base 102 includes the remainder of the substrate 144.

Although the fins 104 have been illustrated in many of the precedingfigures as substantially rectangular with parallel sidewalls, this issimply for ease of illustration, and the fins 104 may have any suitableshape (e.g., shape appropriate to the manufacturing processes used toform the fins 104). For example, as illustrated in the base/finarrangement 158 of FIG. 45, in some embodiments, the fins 104 may betapered. In some embodiments, the fins 104 may taper by 3-10 nanometersin x-width for every 100 nanometers in z-height (e.g., 5 nanometers inx-width for every 100 nanometers in z-height). When the fins 104 aretapered, the wider end of the fins 104 may be the end closest to thebase 102, as illustrated in FIG. 45. FIG. 46 illustrates a particularembodiment of the base/fin arrangement 158 of FIG. 34. In FIG. 46, thequantum well stack 146 is included in the tapered fins 104 while aportion of the substrate 144 is included in the tapered fins and aportion of the substrate 144 provides the base 102.

As noted above, in some embodiments in which the quantum dot device 100includes a fin liner 131, the fin liner 131 may not extend laterallyover the base 102. FIG. 47 is a side cross-sectional view of such anembodiment (analogous to the view of FIG. 1); in particular, FIG. 47illustrates a fin liner 131 on side faces of the fins 104, but notextending laterally over the base 102. The thickness 175 of the finliner 131 in the embodiment of FIG. 47 may take the form of any of theembodiments disclosed herein. To fabricate such a quantum dot device100, a process analogous to formation of the spacers 134 may beperformed to form the fin liners 131 only on side faces of the fins 104.In particular, instead of performing the conformal fin liner depositiondiscussed above with reference to FIG. 7, material for the fin liner 131may be deposited on the assembly 204 (FIG. 6), and then that materialmay be directionally etched “downward” to remove the material for thefin liner 131 on the horizontal surfaces while leaving the material forthe fin liner 131 on the side faces of the fins 104. The fill material128 may be subsequently deposited, and processing may proceed asdescribed above with reference to FIG. 8.

As noted above, a quantum dot device 100 may include multiple fins 104arranged in an array of any desired size. For example, FIG. 48 is a topcross-sectional view, like the view of FIG. 3, of a quantum dot device100 having multiple fins 104 arranged in a two-dimensional array. Magnetlines 121 are not depicted in FIG. 48, although they may be included inany desired arrangements. In the particular example illustrated in FIG.48, the fins 104 may be arranged in pairs, each pair including an“active” fin 104 and a “read” fin 104, as discussed above. Theparticular number and arrangement of fins 104 in FIG. 48 is simplyillustrative, and any desired arrangement may be used. Similarly, aquantum dot device 100 may include multiple sets of fins 104 (andaccompanying gates, as discussed above with reference to FIGS. 1-3)arranged in a two-dimensional array.

As noted above, a single fin 104 may include multiple groups of gates106/108, spaced apart along the fin 104 by a doped region 140. FIG. 49is a cross-sectional view of an example of such a quantum dot device 100having multiple groups of gates 180 at least partially disposed in asingle fin 104, in accordance with various embodiments. Each of thegroups 180 may include gates 106/108 (not labeled in FIG. 49 for ease ofillustration) that may take the form of any of the embodiments of thegates 106/108 discussed herein. A doped region 140 (and its interfacematerial 141) may be disposed between two adjacent groups 180 (labeledin FIG. 49 as groups 180-1 and 180-2), and may provide a commonreservoir for both groups 180. In some embodiments, this “common” dopedregion 140 may be electrically contacted by a single conductive via 136.The particular number of gates 106/108 illustrated in FIG. 49, and theparticular number of groups 180, is simply illustrative, and a fin 104may include any suitable number of gates 106/108 arranged in anysuitable number of groups 180. The quantum dot device 100 of FIG. 49 mayalso include one or more magnet lines 121, arranged as desired.Similarly, in embodiments of the quantum dot device 100 that includefins, a single fin 104 may include multiple groups of gates 106/108,spaced apart along the fin.

As discussed above, in some embodiments in which the gate dielectric 114is not a layer shared commonly between the gates 108 and 106, butinstead is separately deposited on the fins 104 between the spacers 134,the gate dielectric 114 may extend at least partially up the sides ofthe spacers 134, and the gate metal 112 may extend between the portionsof gate dielectric 114 on the spacers 134. FIGS. 50-53 illustratevarious alternative stages in the manufacture of such an embodiment of aquantum dot device 100, in accordance with various embodiments. Inparticular, the operations illustrated in FIGS. 50-53 (as discussedbelow) may take the place of the operations illustrated in FIGS. 13-16.

FIG. 50 is a cross-sectional view of an assembly 1258 subsequent toetching the assembly 212 (FIG. 12) to remove the gate metal 110, and thegate dielectric 114 that is not protected by the patterned hardmask 116,to form the gates 106.

FIG. 51 is a cross-sectional view of an assembly 1260 subsequent toproviding spacers 134 on the sides of the gates 106 (e.g., on the sidesof the hardmask 116, the gate metal 110, and the gate dielectric 114) ofthe assembly 1258 (FIG. 50). The provision of the spacers 134 may takeany of the forms discussed above with reference to FIGS. 14-15, forexample.

FIG. 52 is a cross-sectional view of an assembly 1262 subsequent toproviding a gate dielectric 114 on the fins 104 between the gates 106 ofthe assembly 1260 (FIG. 51). In some embodiments, the gate dielectric114 provided between the gates 106 of the assembly 1260 may be formed byALD and, as illustrated in FIG. 52, may cover the exposed fins 104between the gates 106, and may extend onto the adjacent spacers 134.

FIG. 53 is a cross-sectional view of an assembly 1264 subsequent toproviding the gate metal 112 on the assembly 1262 (FIG. 52). The gatemetal 112 may fill the areas on the fins 104 between adjacent ones ofthe gates 106, and may extend over the tops of the gates 106, as shown.The provision of the gate metal 112 may take any of the forms discussedabove with reference to FIG. 16, for example. The assembly 1264 may befurther processed as discussed above with reference to FIG. 17, forexample.

In some embodiments, the quantum dot device 100 may be included in a dieand coupled to a package substrate to form a quantum dot device package.For example, FIG. 54 is a side cross-sectional view of a die 302including the quantum dot device 100 of FIG. 2 and conductive pathwaylayers 303 disposed thereon, while FIG. 55 is a side cross-sectionalview of a quantum dot device package 300 in which the die 302 andanother die 350 are coupled to a package substrate 304 (e.g., in asystem-on-a-chip (SoC) arrangement). Details of the quantum dot device100 are omitted from FIG. 55 for economy of illustration. As notedabove, the particular quantum dot device 100 illustrated in FIGS. 54 and55 may take a form similar to the embodiment illustrated in FIG. 2, butany of the quantum dot devices 100 disclosed herein may be included in adie (e.g., the die 302) and coupled to a package substrate (e.g., thepackage substrate 304). In particular, any number of fins 104, gates106/108, doped regions 140, magnet lines 121, and other componentsdiscussed herein with reference to various embodiments of the quantumdot device 100 may be included in the die 302.

The die 302 may include a first face 320 and an opposing second face322. The base 102 may be proximate to the second face 322, andconductive pathways 315 from various components of the quantum dotdevice 100 may extend to conductive contacts 365 disposed at the firstface 320. The conductive pathways 315 may include conductive vias,conductive lines, and/or any combination of conductive vias and lines.For example, FIG. 54 illustrates an embodiment in which one conductivepathway 315 (extending between a magnet line 121 and associatedconductive contact 365) includes a conductive via 123, a conductive line393, a conductive via 398, and a conductive line 396. More or fewerstructures may be included in the conductive pathways 315, and analogousconductive pathways 315 may be provided between ones of the conductivecontacts 365 and the gates 106/108, doped regions 140, or othercomponents of the quantum dot device 100. In some embodiments,conductive lines of the die 302 (and the package substrate 304,discussed below) may extend into and out of the plane of the drawing,providing conductive pathways to route electrical signals to and/or fromvarious elements in the die 302.

The conductive vias and/or lines that provide the conductive pathways315 in the die 302 may be formed using any suitable techniques. Examplesof such techniques may include subtractive fabrication techniques,additive or semi-additive fabrication techniques, single Damascenefabrication techniques, dual Damascene fabrication techniques, or anyother suitable technique. In some embodiments, layers of oxide material390 and layers of nitride material 391 may insulate various structuresin the conductive pathways 315 from proximate structures, and/or mayserve as etch stops during fabrication. In some embodiments, an adhesionlayer (not shown) may be disposed between conductive material andproximate insulating material of the die 302 to improve mechanicaladhesion between the conductive material and the insulating material.

The gates 106/108, the doped regions 140, and the quantum well stack 146(as well as the proximate conductive vias/lines) may be referred to aspart of the “device layer” of the quantum dot device 100. The conductivelines 393 may be referred to as a Metal 1 or “M1” interconnect layer,and may couple the structures in the device layer to other interconnectstructures. The conductive vias 398 and the conductive lines 396 may bereferred to as a Metal 2 or “M2” interconnect layer, and may be formeddirectly on the M1 interconnect layer.

A solder resist material 367 may be disposed around the conductivecontacts 365, and, in some embodiments, may extend onto the conductivecontacts 365. The solder resist material 367 may be a polyimide orsimilar material, or may be any appropriate type of packaging solderresist material. In some embodiments, the solder resist material 367 maybe a liquid or dry film material including photoimageable polymers. Insome embodiments, the solder resist material 367 may benon-photoimageable (and openings therein may be formed using laserdrilling or masked etch techniques). The conductive contacts 365 mayprovide the contacts to couple other components (e.g., a packagesubstrate 304, as discussed below, or another component) to theconductive pathways 315 in the quantum dot device 100, and may be formedof any suitable conductive material (e.g., a superconducting material).For example, solder bonds may be formed on the one or more conductivecontacts 365 to mechanically and/or electrically couple the die 302 withanother component (e.g., a circuit board), as discussed below. Theconductive contacts 365 illustrated in FIG. 54 take the form of bondpads, but other first-level interconnect structures may be used (e.g.,posts) to route electrical signals to/from the die 302, as discussedbelow.

The combination of the conductive pathways and the proximate insulatingmaterial (e.g., the insulating material 130, the oxide material 390, andthe nitride material 391) in the die 302 may provide an interlayerdielectric (ILD) stack of the die 302. As noted above, interconnectstructures may be arranged within the quantum dot device 100 to routeelectrical signals according to a wide variety of designs (inparticular, the arrangement is not limited to the particularconfiguration of interconnect structures depicted in FIG. 54 or any ofthe other accompanying figures, and may include more or fewerinterconnect structures). During operation of the quantum dot device100, electrical signals (such as power and/or input/output (I/O)signals) may be routed to and/or from the gates 106/108, the magnetline(s) 121, and/or the doped regions 140 (and/or other components) ofthe quantum dot device 100 through the interconnects provided byconductive vias and/or lines, and through the conductive pathways of thepackage substrate 304 (discussed below).

Example superconducting materials that may be used for the structures inthe conductive pathways 313, 317, 319 (discussed below), and 315, and/orconductive contacts of the die 302 and/or the package substrate 304, mayinclude aluminum, niobium, tin, titanium, osmium, zinc, molybdenum,tantalum, vanadium, or composites of such materials (e.g., niobiumtitanium, niobium aluminum, or niobium tin). In some embodiments, theconductive contacts 365, 379, and/or 399 may include aluminum, and thefirst-level interconnects 306 and/or the second-level interconnects 308may include an indium-based solder.

As noted above, the quantum dot device package 300 of FIG. 55 mayinclude a die 302 (including one or more quantum dot devices 100) and adie 350. As discussed in detail below, the quantum dot device package300 may include electrical pathways between the die 302 and the die 350so that the dies 302 and 350 may communicate during operation. In someembodiments, the die 350 may be a non-quantum logic device that mayprovide support or control functionality for the quantum dot device(s)100 of the die 302. For example, as discussed further below, in someembodiments, the die 350 may include a switching matrix to control thewriting and reading of data from the die 302 (e.g., using any known wordline/bit line or other addressing architecture). In some embodiments,the die 350 may control the voltages (e.g., microwave pulses) applied tothe gates 106/108, and/or the doped regions 140, of the quantum dotdevice(s) 100 included in the die 302. In some embodiments, the die 350may include magnet line control logic to provide microwave pulses to themagnet line(s) 121 of the quantum dot device(s) 100 in the die 302. Thedie 350 may include any desired control circuitry to support operationof the die 302. By including this control circuitry in a separate die,the manufacture of the die 302 may be simplified and focused on theneeds of the quantum computations performed by the quantum dot device(s)100, and conventional manufacturing and design processes for controllogic (e.g., switching array logic) may be used to form the die 350.

Although a singular “die 350” is illustrated in FIG. 55 and discussedherein, the functionality provided by the die 350 may, in someembodiments, be distributed across multiple dies 350 (e.g., multipledies coupled to the package substrate 304, or otherwise sharing a commonsupport with the die 302). Similarly, one or more dies providing thefunctionality of the die 350 may support one or more dies providing thefunctionality of the die 302; for example, the quantum dot devicepackage 300 may include multiple dies having one or more quantum dotdevices 100, and a die 350 may communicate with one or more such“quantum dot device dies.”

The die 350 may take any of the forms discussed below with reference tothe non-quantum processing device 2028 of FIG. 59. Mechanisms by whichthe control logic of the die 350 may control operation of the die 302may be take the form of an entirely hardware embodiment or an embodimentcombining software and hardware aspects. For example, the die 350 mayimplement an algorithm executed by one or more processing units, e.g.one or more microprocessors. In various embodiments, aspects of thepresent disclosure may take the form of a computer program productembodied in one or more computer readable medium(s), preferablynon-transitory, having computer readable program code embodied (e.g.,stored) in or coupled to the die 350. In various embodiments, such acomputer program may, for example, be downloaded (updated) to the die350 (or attendant memory) or be stored upon manufacturing of the die350. In some embodiments, the die 350 may include at least one processorand at least one memory element, along with any other suitable hardwareand/or software to enable its intended functionality of controllingoperation of the die 302 as described herein. A processor of the die 350may execute software or an algorithm to perform the activities discussedherein. A processor of the die 350 may be communicatively coupled toother system elements via one or more interconnects or buses (e.g.,through one or more conductive pathways 319). Such a processor mayinclude any combination of hardware, software, or firmware providingprogrammable logic, including by way of non-limiting example, amicroprocessor, a digital signal processor (DSP), a field-programmablegate array (FPGA), a programmable logic array (PLA), anapplication-specific integrated circuit (ASIC), or a virtual machineprocessor. The processor of the die 350 may be communicatively coupledto the memory element of the die 350, for example, in a direct-memoryaccess (DMA) configuration. A memory element of the die 350 may includeany suitable volatile or nonvolatile memory technology, including doubledata rate (DDR) random access memory (RAM), synchronous RAM (SRAM),dynamic RAM (DRAM), flash, read-only memory (ROM), optical media,virtual memory regions, magnetic or tape memory, or any other suitabletechnology. In some embodiments, the memory element and the processor ofthe “die 350” may themselves be provided by separate physical dies thatare in electrical communication. The information being tracked or sentto the die 350 could be provided in any database, register, controllist, cache, or storage structure, all of which can be referenced at anysuitable timeframe. The die 350 can further include suitable interfacesfor receiving, transmitting, and/or otherwise communicating data orinformation in a network environment (e.g., via the conductive pathways319).

In some embodiments, the die 350 may be configured to apply appropriatevoltages to any one of the gates 106/108 (acting as, e.g., plungergates, barrier gates, and/or accumulation gates) in order to initializeand manipulate the quantum dots 142, as discussed above. For example, bycontrolling the voltage applied to a gate 106/108 acting as a plungergate, the die 350 may modulate the electric field underneath that gateto create an energy valley between the tunnel barriers created byadjacent barrier gates. In another example, by controlling the voltageapplied to a gate 106/108 acting as a barrier gate, the die 350 maychange the height of the tunnel barrier. When a barrier gate is used toset a tunnel barrier between two plunger gates, the barrier gate may beused to transfer charge carriers between quantum dots 142 that may beformed under these plunger gates. When a barrier gate is used to set atunnel barrier between a plunger gate and an accumulation gate, thebarrier gate may be used to transfer charge carriers in and out of thequantum dot array via the accumulation gate. The term “accumulationgate” may refer to a gate used to form a 2DEG in an area that is betweenthe area where the quantum dots 142 may be formed and a charge carrierreservoir (e.g., the doped regions 140). Changing the voltage applied tothe accumulation gate may allow the die 350 to control the number ofcharge carriers in the area under the accumulation gate. For example,changing the voltage applied to the accumulation gate may reduce thenumber of charge carriers in the area under the gate so that singlecharge carriers can be transferred from the reservoir into the quantumwell layer 152, and vice versa. In some embodiments, the “outermost”gates 106 in a quantum dot device 100 may serve as accumulation gates.In some embodiments, these outermost gates 106 may have a greater length168 than “inner” gates 106.

As noted above, the die 350 may provide electrical signals to controlspins of charge carriers in quantum dots 142 of the quantum dotdevice(s) 100 of the die 302 by controlling a magnetic field generatedby one or more magnet line(s) 121. In this manner, the die 350 mayinitialize and manipulate spins of the charge carriers in the quantumdots 142 to implement qubit operations. If the magnetic field for a die302 is generated by a microwave transmission line, then the die 350 mayset/manipulate the spins of the charge carriers by applying appropriatepulse sequences to manipulate spin precession. Alternatively, themagnetic field for a quantum dot device 100 of the die 302 may begenerated by a magnet with one or more pulsed gates; the die 350 mayapply the pulses to these gates.

In some embodiments, the die 350 may be configured to determine thevalues of the control signals applied to the elements of the die 302(e.g. determine the voltages to be applied to the various gates 106/108)to achieve desired quantum operations (communicated to the die 350through the package substrate 304 via the conductive pathways 319). Inother embodiments, the die 350 may be preprogrammed with at least someof the control parameters (e.g. with the values for the voltages to beapplied to the various gates 106/108) during the initialization of thedie 350.

In the quantum dot device package 300 (FIG. 55), first-levelinterconnects 306 may be disposed between the first face 320 of the die302 and the second face 326 of a package substrate 304. Havingfirst-level interconnects 306 disposed between the first face 320 of thedie 302 and the second face 326 of the package substrate 304 (e.g.,using solder bumps as part of flip chip packaging techniques) may enablethe quantum dot device package 300 to achieve a smaller footprint andhigher die-to-package-substrate connection density than could beachieved using conventional wirebond techniques (in which conductivecontacts between the die 302 and the package substrate 304 areconstrained to be located on the periphery of the die 302). For example,a die 302 having a square first face 320 with side length N may be ableto form only 4N wirebond interconnects to the package substrate 304,versus N² flip chip interconnects (utilizing the entire “full field”surface area of the first face 320). Additionally, in some applications,wirebond interconnects may generate unacceptable amounts of heat thatmay damage or otherwise interfere with the performance of the quantumdot device 100. Using solder bumps as the first-level interconnects 306may enable the quantum dot device package 300 to have much lowerparasitic inductance relative to using wirebonds to couple the die 302and the package substrate 304, which may result in an improvement insignal integrity for high speed signals communicated between the die 302and the package substrate 304. Similarly, first-level interconnects 309may be disposed between conductive contacts 371 of the die 350 andconductive contacts 379 at the second face 326 of the package substrate304, as shown, to couple electronic components (not shown) in the die350 to conductive pathways in the package substrate 304.

The package substrate 304 may include a first face 324 and an opposingsecond face 326. Conductive contacts 399 may be disposed at the firstface 324, and conductive contacts 379 may be disposed at the second face326. Solder resist material 314 may be disposed around the conductivecontacts 379, and solder resist material 312 may be disposed around theconductive contacts 399; the solder resist materials 314 and 312 maytake any of the forms discussed above with reference to the solderresist material 367. In some embodiments, the solder resist material 312and/or the solder resist material 314 may be omitted. Conductivepathways may extend through the insulating material 310 between thefirst face 324 and the second face 326 of the package substrate 304,electrically coupling various ones of the conductive contacts 399 tovarious ones of the conductive contacts 379, in any desired manner. Theinsulating material 310 may be a dielectric material (e.g., an ILD), andmay take the form of any of the embodiments of the insulating material130 disclosed herein, for example. The conductive pathways may includeone or more conductive vias 395 and/or one or more conductive lines 397,for example.

For example, the package substrate 304 may include one or moreconductive pathways 313 to electrically couple the die 302 to conductivecontacts 399 on the first face 324 of the package substrate 304; theseconductive pathways 313 may be used to allow the die 302 to electricallycommunicate with a circuit component to which the quantum dot devicepackage 300 is coupled (e.g., a circuit board or interposer, asdiscussed below). The package substrate 304 may include one or moreconductive pathways 319 to electrically couple the die 350 to conductivecontacts 399 on the first face 324 of the package substrate 304; theseconductive pathways 319 may be used to allow the die 350 to electricallycommunicate with a circuit component to which the quantum dot devicepackage 300 is coupled (e.g., a circuit board or interposer, asdiscussed below).

The package substrate 304 may include one or more conductive pathways317 to electrically couple the die 302 to the die 350 through thepackage substrate 304. In particular, the package substrate 304 mayinclude conductive pathways 317 that couple different ones of theconductive contacts 379 on the second face 326 of the package substrate304 so that, when the die 302 and the die 350 are coupled to thesedifferent conductive contacts 379, the die 302 and the die 350 maycommunicate through the package substrate 304. Although the die 302 andthe die 350 are illustrated in FIG. 55 as being disposed on the samesecond face 326 of the package substrate 304, in some embodiments, thedie 302 and the die 350 may be disposed on different faces of thepackage substrate 304 (e.g., one on the first face 324 and one on thesecond face 326), and may communicate via one or more conductivepathways 317.

In some embodiments, the conductive pathways 317 may be microwavetransmission lines. Microwave transmission lines may be structured forthe effective transmission of microwave signals, and may take the formof any microwave transmission lines known in the art. For example, aconductive pathway 317 may be a coplanar waveguide, a stripline, amicrostrip line, or an inverted microstrip line. The die 350 may providemicrowave pulses along the conductive pathways 317 to the die 302 toprovide electron spin resonance (ESR) pulses to the quantum dotdevice(s) 100 to manipulate the spin states of the quantum dots 142 thatform therein. In some embodiments, the die 350 may generate a microwavepulse that is transmitted over a conductive pathway 317 and induces amagnetic field in the magnet line(s) 121 of a quantum dot device 100 andcauses a transition between the spin-up and spin-down states of aquantum dot 142. In some embodiments, the die 350 may generate amicrowave pulse that is transmitted over a conductive pathway 317 andinduces a magnetic field in a gate 106/108 to cause a transition betweenthe spin-up and spin-down states of a quantum dot 142. The die 350 mayenable any such embodiments, or any combination of such embodiments.

The die 350 may provide any suitable control signals to the die 302 toenable operation of the quantum dot device(s) 100 included in the die302. For example, the die 350 may provide voltages (through theconductive pathways 317) to the gates 106/108, and thereby tune theenergy profile in the quantum well stack 146.

In some embodiments, the quantum dot device package 300 may be a coredpackage, one in which the package substrate 304 is built on a carriermaterial (not shown) that remains in the package substrate 304. In suchembodiments, the carrier material may be a dielectric material that ispart of the insulating material 310; laser vias or other through-holesmay be made through the carrier material to allow conductive pathways313 and/or 319 to extend between the first face 324 and the second face326.

In some embodiments, the package substrate 304 may be or may otherwiseinclude a silicon interposer, and the conductive pathways 313 and/or 319may be through-silicon vias. Silicon may have a desirably lowcoefficient of thermal expansion compared with other dielectricmaterials that may be used for the insulating material 310, and thus maylimit the degree to which the package substrate 304 expands andcontracts during temperature changes relative to such other materials(e.g., polymers having higher coefficients of thermal expansion). Asilicon interposer may also help the package substrate 304 achieve adesirably small line width and maintain high connection density to thedie 302 and/or the die 350.

Limiting differential expansion and contraction may help preserve themechanical and electrical integrity of the quantum dot device package300 as the quantum dot device package 300 is fabricated (and exposed tohigher temperatures) and used in a cooled environment (and exposed tolower temperatures). In some embodiments, thermal expansion andcontraction in the package substrate 304 may be managed by maintainingan approximately uniform density of the conductive material in thepackage substrate 304 (so that different portions of the packagesubstrate 304 expand and contract uniformly), using reinforceddielectric materials as the insulating material 310 (e.g., dielectricmaterials with silicon dioxide fillers), or utilizing stiffer materialsas the insulating material 310 (e.g., a prepreg material including glasscloth fibers). In some embodiments, the die 350 may be formed ofsemiconductor materials or compound semiconductor materials (e.g., groupIII-group V compounds) to enable higher efficiency amplification andsignal generation to minimize the heat generated during operation andreduce the impact on the quantum operations of the die 302. In someembodiments, the metallization in the die 350 may use superconductingmaterials (e.g., titanium nitride, niobium, niobium nitride, and niobiumtitanium nitride) to minimize heating.

The conductive contacts 365 of the die 302 may be electrically coupledto the conductive contacts 379 of the package substrate 304 via thefirst-level interconnects 306, and the conductive contacts 371 of thedie 350 may be electrically coupled to the conductive contacts 379 ofthe package substrate 304 via the first-level interconnects 309. In someembodiments, the first-level interconnects 306/309 may include solderbumps or balls (as illustrated in FIG. 55); for example, the first-levelinterconnects 306/309 may be flip chip (or controlled collapse chipconnection, “C4”) bumps disposed initially on the die 302/die 350 or onthe package substrate 304. Second-level interconnects 308 (e.g., solderballs or other types of interconnects) may couple the conductivecontacts 399 on the first face 324 of the package substrate 304 toanother component, such as a circuit board (not shown). Examples ofarrangements of electronics packages that may include an embodiment ofthe quantum dot device package 300 are discussed below with reference toFIG. 57. The die 302 and/or the die 350 may be brought in contact withthe package substrate 304 using a pick-and-place apparatus, for example,and a reflow or thermal compression bonding operation may be used tocouple the die 302 and/or the die 350 to the package substrate 304 viathe first-level interconnects 306 and/or the first-level interconnects309, respectively.

The conductive contacts 365, 371, 379, and/or 399 may include multiplelayers of material that may be selected to serve different purposes. Insome embodiments, the conductive contacts 365, 371, 379, and/or 399 maybe formed of aluminum, and may include a layer of gold (e.g., with athickness of less than 1 micron) between the aluminum and the adjacentinterconnect to limit the oxidation of the surface of the contacts andimprove the adhesion with adjacent solder. In some embodiments, theconductive contacts 365, 371, 379, and/or 399 may be formed of aluminum,and may include a layer of a barrier metal such as nickel, as well as alayer of gold, wherein the layer of barrier metal is disposed betweenthe aluminum and the layer of gold, and the layer of gold is disposedbetween the barrier metal and the adjacent interconnect. In suchembodiments, the gold may protect the barrier metal surface fromoxidation before assembly, and the barrier metal may limit the diffusionof solder from the adjacent interconnects into the aluminum.

In some embodiments, the structures and materials in the quantum dotdevice 100 may be damaged if the quantum dot device 100 is exposed tothe high temperatures that are common in conventional integrated circuitprocessing (e.g., greater than 100 degrees Celsius, or greater than 200degrees Celsius). In particular, in embodiments in which the first-levelinterconnects 306/309 include solder, the solder may be a lowtemperature solder (e.g., a solder having a melting point below 100degrees Celsius) so that it can be melted to couple the conductivecontacts 365/371 and the conductive contacts 379 without having toexpose the die 302 to higher temperatures and risk damaging the quantumdot device 100. Examples of solders that may be suitable includeindium-based solders (e.g., solders including indium alloys). When lowtemperature solders are used, however, these solders may not be fullysolid during handling of the quantum dot device package 300 (e.g., atroom temperature or temperatures between room temperature and 100degrees Celsius), and thus the solder of the first-level interconnects306/309 alone may not reliably mechanically couple the die 302/die 350and the package substrate 304 (and thus may not reliably electricallycouple the die 302/die 350 and the package substrate 304). In some suchembodiments, the quantum dot device package 300 may further include amechanical stabilizer to maintain mechanical coupling between the die302/die 350 and the package substrate 304, even when solder of thefirst-level interconnects 306/309 is not solid. Examples of mechanicalstabilizers may include an underfill material disposed between the die302/die 350 and the package substrate 304, a corner glue disposedbetween the die 302/die 350 and the package substrate 304, an overmoldmaterial disposed around the die 302/die 350 on the package substrate304, and/or a mechanical frame to secure the die 302/die 350 and thepackage substrate 304.

In some embodiments of the quantum dot device package 300, the die 350may not be included in the package 300; instead, the die 350 may beelectrically coupled to the die 302 through another type of commonphysical support. For example, the die 350 may be separately packagedfrom the die 302 (e.g., the die 350 may be mounted to its own packagesubstrate), and the two packages may be coupled together through aninterposer, a printed circuit board, a bridge, a package-on-packagearrangement, or in any other manner. Examples of device assemblies thatmay include the die 302 and the die 350 in various arrangements arediscussed below with reference to FIG. 57.

FIGS. 56A-B are top views of a wafer 450 and dies 452 that may be formedfrom the wafer 450; the dies 452 may be included in any of the quantumdot device packages (e.g., the quantum dot device package 300) disclosedherein. The wafer 450 may include semiconductor material and may includeone or more dies 452 having conventional and quantum dot device elementsformed on a surface of the wafer 450. Each of the dies 452 may be arepeating unit of a semiconductor product that includes any suitableconventional and/or quantum dot device. After the fabrication of thesemiconductor product is complete, the wafer 450 may undergo asingulation process in which each one of the dies 452 is separated fromthe others to provide discrete “chips” of the semiconductor product. Adie 452 may include one or more quantum dot devices 100 and/orsupporting circuitry to route electrical signals to the quantum dotdevices 100 (e.g., interconnects including conductive vias and lines),as well as any other integrated circuit (IC) components. In someembodiments, the wafer 450 or the die 452 may include a memory device(e.g., a static random access memory (SRAM) device), a logic device(e.g., AND, OR, NAND, or NOR gate), or any other suitable circuitelement. Multiple ones of these devices may be combined on a single die452. For example, a memory array formed by multiple memory devices maybe formed on a same die 452 as a processing device (e.g., the processingdevice 2002 of FIG. 59) or other logic that is configured to storeinformation in the memory devices or execute instructions stored in thememory array.

FIG. 57 is a cross-sectional side view of a device assembly 400 that mayinclude any of the embodiments of the quantum dot device packages 300disclosed herein. The device assembly 400 includes a number ofcomponents disposed on a circuit board 402. The device assembly 400 mayinclude components disposed on a first face 440 of the circuit board 402and an opposing second face 442 of the circuit board 402; generally,components may be disposed on one or both faces 440 and 442.

In some embodiments, the circuit board 402 may be a printed circuitboard (PCB) including multiple metal layers separated from one anotherby layers of dielectric material and interconnected by electricallyconductive vias. Any one or more of the metal layers may be formed in adesired circuit pattern to route electrical signals (optionally inconjunction with other metal layers) between the components coupled tothe circuit board 402. In other embodiments, the circuit board 402 maybe a package substrate or flexible board. In some embodiments, the die302 and the die 350 (FIG. 55) may be separately packaged and coupledtogether via the circuit board 402 (e.g., the conductive pathways 317may run through the circuit board 402).

The device assembly 400 illustrated in FIG. 57 includes apackage-on-interposer structure 436 coupled to the first face 440 of thecircuit board 402 by coupling components 416. The coupling components416 may electrically and mechanically couple the package-on-interposerstructure 436 to the circuit board 402, and may include solder balls (asshown in FIG. 55), male and female portions of a socket, an adhesive, anunderfill material, and/or any other suitable electrical and/ormechanical coupling structure.

The package-on-interposer structure 436 may include a package 420coupled to an interposer 404 by coupling components 418. The couplingcomponents 418 may take any suitable form for the application, such asthe forms discussed above with reference to the coupling components 416.For example, the coupling components 418 may be the second-levelinterconnects 308. Although a single package 420 is shown in FIG. 57,multiple packages may be coupled to the interposer 404; indeed,additional interposers may be coupled to the interposer 404. Theinterposer 404 may provide an intervening substrate used to bridge thecircuit board 402 and the package 420. The package 420 may be a quantumdot device package 300 or may be a conventional IC package, for example.In some embodiments, the package 420 may take the form of any of theembodiments of the quantum dot device package 300 disclosed herein, andmay include a quantum dot device die 302 coupled to a package substrate304 (e.g., by flip chip connections). Generally, the interposer 404 mayspread a connection to a wider pitch or reroute a connection to adifferent connection. For example, the interposer 404 may couple thepackage 420 (e.g., a die) to a ball grid array (BGA) of the couplingcomponents 416 for coupling to the circuit board 402. In the embodimentillustrated in FIG. 57, the package 420 and the circuit board 402 areattached to opposing sides of the interposer 404; in other embodiments,the package 420 and the circuit board 402 may be attached to a same sideof the interposer 404. In some embodiments, three or more components maybe interconnected by way of the interposer 404. In some embodiments, aquantum dot device package 300 including the die 302 and the die 350(FIG. 55) may be one of the packages disposed on an interposer like theinterposer 404. In some embodiments, the die 302 and the die 350 (FIG.55) may be separately packaged and coupled together via the interposer404 (e.g., the conductive pathways 317 may run through the interposer404).

The interposer 404 may be formed of an epoxy resin, afiberglass-reinforced epoxy resin, a ceramic material, or a polymermaterial such as polyimide. In some embodiments, the interposer 404 maybe formed of alternate rigid or flexible materials that may include thesame materials described above for use in a semiconductor substrate,such as silicon, germanium, and other group III-group V compounds andgroup IV materials. The interposer 404 may include metal interconnects408 and vias 410, including but not limited to through-silicon vias(TSVs) 406. The interposer 404 may further include embedded devices 414,including both passive and active devices. Such devices may include, butare not limited to, capacitors, decoupling capacitors, resistors,inductors, fuses, diodes, transformers, sensors, electrostatic discharge(ESD) devices, and memory devices. More complex devices such as radiofrequency (RF) devices, power amplifiers, power management devices,antennas, arrays, sensors, and microelectromechanical systems (MEMS)devices may also be formed on the interposer 404. Thepackage-on-interposer structure 436 may take the form of any of thepackage-on-interposer structures known in the art.

The device assembly 400 may include a package 424 coupled to the firstface 440 of the circuit board 402 by coupling components 422. Thecoupling components 422 may take the form of any of the embodimentsdiscussed above with reference to the coupling components 416, and thepackage 424 may take the form of any of the embodiments discussed abovewith reference to the package 420. The package 424 may be a quantum dotdevice package 300 (e.g., including the die 302 and the die 350, or justthe die 302) or may be a conventional IC package, for example. In someembodiments, the package 424 may take the form of any of the embodimentsof the quantum dot device package 300 disclosed herein, and may includea quantum dot device die 302 coupled to a package substrate 304 (e.g.,by flip chip connections).

The device assembly 400 illustrated in FIG. 57 includes apackage-on-package structure 434 coupled to the second face 442 of thecircuit board 402 by coupling components 428. The package-on-packagestructure 434 may include a package 426 and a package 432 coupledtogether by coupling components 430 such that the package 426 isdisposed between the circuit board 402 and the package 432. The couplingcomponents 428 and 430 may take the form of any of the embodiments ofthe coupling components 416 discussed above, and the packages 426 and432 may take the form of any of the embodiments of the package 420discussed above. Each of the packages 426 and 432 may be a quantum dotdevice package 300 or may be a conventional IC package, for example. Insome embodiments, one or both of the packages 426 and 432 may take theform of any of the embodiments of the quantum dot device package 300disclosed herein, and may include a die 302 coupled to a packagesubstrate 304 (e.g., by flip chip connections). In some embodiments, aquantum dot device package 300 including the die 302 and the die 350(FIG. 55) may be one of the packages in a package-on-package structurelike the package-on-package structure 434. In some embodiments, the die302 and the die 350 (FIG. 55) may be separately packaged and coupledtogether using a package-on-package structure like thepackage-on-package structure 434 (e.g., the conductive pathways 317 mayrun through a package substrate of one or both of the packages of thedies 302 and 350).

A number of techniques are disclosed herein for operating a quantum dotdevice 100. FIG. 58 is a flow diagram of a particular illustrativemethod 1020 of operating a quantum dot device, in accordance withvarious embodiments. Although the operations discussed below withreference to the method 1020 are illustrated in a particular order anddepicted once each, these operations may be repeated or performed in adifferent order (e.g., in parallel), as suitable. Additionally, variousoperations may be omitted, as suitable. Various operations of the method1020 may be illustrated with reference to one or more of the embodimentsdiscussed above, but the method 1020 may be used to operate any suitablequantum dot device (including any suitable ones of the embodimentsdisclosed herein).

At 1022, electrical signals may be provided to one or more first gatesdisposed above a quantum well stack as part of causing a first quantumwell to form in a quantum well layer in the quantum well stack. Thequantum well stack may take the form of any of the embodiments disclosedherein (e.g., the quantum well stacks 146 discussed above with referenceto FIGS. 37-39), and may be included in any of the quantum dot devices100 disclosed herein. For example, a voltage may be applied to a gate108-11 as part of causing a first quantum well (for a first quantum dot142) to form in the quantum well stack 146 below the gate 108-11.

At 1024, electrical signals may be provided to one or more second gatesdisposed above the quantum well stack as part of causing a secondquantum well to form in the quantum well layer. For example, a voltagemay be applied to the gate 108-12 as part of causing a second quantumwell (for a second quantum dot 142) to form in the quantum well stack146 below the gate 108-12.

At 1026, electrical signals may be provided to one or more third gatesdisposed above the quantum well stack as part of (1) causing a thirdquantum well to form in the quantum well layer or (2) providing apotential barrier between the first quantum well and the second quantumwell. For example, a voltage may be applied to the gate 106-12 as partof (1) causing a third quantum well (for a third quantum dot 142) toform in the quantum well stack 146 below the gate 106-12 (e.g., when thegate 106-12 acts as a “plunger” gate) or (2) providing a potentialbarrier between the first quantum well (under the gate 108-11) and thesecond quantum well (under the gate 108-12) (e.g., when the gate 106-12acts as a “barrier” gate).

FIG. 59 is a block diagram of an example quantum computing device 2000that may include any of the quantum dot devices disclosed herein. Anumber of components are illustrated in FIG. 59 as included in thequantum computing device 2000, but any one or more of these componentsmay be omitted or duplicated, as suitable for the application. In someembodiments, some or all of the components included in the quantumcomputing device 2000 may be attached to one or more PCBs (e.g., amotherboard). In some embodiments, various ones of these components maybe fabricated onto a single SoC die. Additionally, in variousembodiments, the quantum computing device 2000 may not include one ormore of the components illustrated in FIG. 59, but the quantum computingdevice 2000 may include interface circuitry for coupling to the one ormore components. For example, the quantum computing device 2000 may notinclude a display device 2006, but may include display device interfacecircuitry (e.g., a connector and driver circuitry) to which a displaydevice 2006 may be coupled. In another set of examples, the quantumcomputing device 2000 may not include an audio input device 2024 or anaudio output device 2008, but may include audio input or output deviceinterface circuitry (e.g., connectors and supporting circuitry) to whichan audio input device 2024 or audio output device 2008 may be coupled.

The quantum computing device 2000 may include a processing device 2002(e.g., one or more processing devices). As used herein, the term“processing device” or “processor” may refer to any device or portion ofa device that processes electronic data from registers and/or memory totransform that electronic data into other electronic data that may bestored in registers and/or memory. The processing device 2002 mayinclude a quantum processing device 2026 (e.g., one or more quantumprocessing devices), and a non-quantum processing device 2028 (e.g., oneor more non-quantum processing devices). The quantum processing device2026 may include one or more of the quantum dot devices 100 disclosedherein, and may perform data processing by performing operations on thequantum dots that may be generated in the quantum dot devices 100, andmonitoring the result of those operations. For example, as discussedabove, different quantum dots may be allowed to interact, the quantumstates of different quantum dots may be set or transformed, and thequantum states of quantum dots may be read (e.g., by another quantumdot). The quantum processing device 2026 may be a universal quantumprocessor, or specialized quantum processor configured to run one ormore particular quantum algorithms. In some embodiments, the quantumprocessing device 2026 may execute algorithms that are particularlysuitable for quantum computers, such as cryptographic algorithms thatutilize prime factorization, encryption/decryption, algorithms tooptimize chemical reactions, algorithms to model protein folding, etc.The quantum processing device 2026 may also include support circuitry tosupport the processing capability of the quantum processing device 2026,such as input/output channels, multiplexers, signal mixers, quantumamplifiers, and analog-to-digital converters. For example, the quantumprocessing device 2026 may include circuitry (e.g., a current source) toprovide current pulses to one or more magnet lines 121 included in thequantum dot device 100.

As noted above, the processing device 2002 may include a non-quantumprocessing device 2028. In some embodiments, the non-quantum processingdevice 2028 may provide peripheral logic to support the operation of thequantum processing device 2026. For example, the non-quantum processingdevice 2028 may control the performance of a read operation, control theperformance of a write operation, control the clearing of quantum bits,etc. The non-quantum processing device 2028 may also performconventional computing functions to supplement the computing functionsprovided by the quantum processing device 2026. For example, thenon-quantum processing device 2028 may interface with one or more of theother components of the quantum computing device 2000 (e.g., thecommunication chip 2012 discussed below, the display device 2006discussed below, etc.) in a conventional manner, and may serve as aninterface between the quantum processing device 2026 and conventionalcomponents. The non-quantum processing device 2028 may include one ormore DSPs, ASICs, central processing units (CPUs), graphics processingunits (GPUs), cryptoprocessors (specialized processors that executecryptographic algorithms within hardware), server processors, or anyother suitable processing devices.

The quantum computing device 2000 may include a memory 2004, which mayitself include one or more memory devices such as volatile memory (e.g.,dynamic random access memory (DRAM)), nonvolatile memory (e.g., ROM),flash memory, solid state memory, and/or a hard drive. In someembodiments, the states of qubits in the quantum processing device 2026may be read and stored in the memory 2004. In some embodiments, thememory 2004 may include memory that shares a die with the non-quantumprocessing device 2028. This memory may be used as cache memory and mayinclude embedded dynamic random access memory (eDRAM) or spin transfertorque magnetic random access memory (STT-M RAM).

The quantum computing device 2000 may include a cooling apparatus 2030.The cooling apparatus 2030 may maintain the quantum processing device2026 at a predetermined low temperature during operation to reduce theeffects of scattering in the quantum processing device 2026. Thispredetermined low temperature may vary depending on the setting; in someembodiments, the temperature may be 5 Kelvin or less. In someembodiments, the non-quantum processing device 2028 (and various othercomponents of the quantum computing device 2000) may not be cooled bythe cooling apparatus 2030, and may instead operate at room temperature.The cooling apparatus 2030 may be, for example, a dilution refrigerator,a helium-3 refrigerator, or a liquid helium refrigerator.

In some embodiments, the quantum computing device 2000 may include acommunication chip 2012 (e.g., one or more communication chips). Forexample, the communication chip 2012 may be configured for managingwireless communications for the transfer of data to and from the quantumcomputing device 2000. The term “wireless” and its derivatives may beused to describe circuits, devices, systems, methods, techniques,communications channels, etc., that may communicate data through the useof modulated electromagnetic radiation through a nonsolid medium. Theterm does not imply that the associated devices do not contain anywires, although in some embodiments they might not.

The communication chip 2012 may implement any of a number of wirelessstandards or protocols, including but not limited to Institute forElectrical and Electronic Engineers (IEEE) standards including Wi-Fi(IEEE 802.11 family), IEEE 802.16 standards (e.g., IEEE 802.16-2005Amendment), Long-Term Evolution (LTE) project along with any amendments,updates, and/or revisions (e.g., advanced LTE project, ultramobilebroadband (UMB) project (also referred to as “3GPP2”), etc.). IEEE802.16 compatible Broadband Wireless Access (BWA) networks are generallyreferred to as WiMAX networks, an acronym that stands for WorldwideInteroperability for Microwave Access, which is a certification mark forproducts that pass conformity and interoperability tests for the IEEE802.16 standards. The communication chip 2012 may operate in accordancewith a Global System for Mobile Communication (GSM), General PacketRadio Service (GPRS), Universal Mobile Telecommunications System (UMTS),High Speed Packet Access (HSPA), Evolved HSPA (E-HSPA), or LTE network.The communication chip 2012 may operate in accordance with Enhanced Datafor GSM Evolution (EDGE), GSM EDGE Radio Access Network (GERAN),Universal Terrestrial Radio Access Network (UTRAN), or Evolved UTRAN(E-UTRAN). The communication chip 2012 may operate in accordance withCode Division Multiple Access (CDMA), Time Division Multiple Access(TDMA), Digital Enhanced Cordless Telecommunications (DECT),Evolution-Data Optimized (EV-DO), and derivatives thereof, as well asany other wireless protocols that are designated as 3G, 4G, 5G, andbeyond. The communication chip 2012 may operate in accordance with otherwireless protocols in other embodiments. The quantum computing device2000 may include an antenna 2022 to facilitate wireless communicationsand/or to receive other wireless communications (such as AM or FM radiotransmissions).

In some embodiments, the communication chip 2012 may manage wiredcommunications, such as electrical, optical, or any other suitablecommunication protocols (e.g., the Ethernet). As noted above, thecommunication chip 2012 may include multiple communication chips. Forinstance, a first communication chip 2012 may be dedicated toshorter-range wireless communications such as Wi-Fi or Bluetooth, and asecond communication chip 2012 may be dedicated to longer-range wirelesscommunications such as global positioning system (GPS), EDGE, GPRS,CDMA, WiMAX, LTE, EV-DO, or others. In some embodiments, a firstcommunication chip 2012 may be dedicated to wireless communications, anda second communication chip 2012 may be dedicated to wiredcommunications.

The quantum computing device 2000 may include battery/power circuitry2014. The battery/power circuitry 2014 may include one or more energystorage devices (e.g., batteries or capacitors) and/or circuitry forcoupling components of the quantum computing device 2000 to an energysource separate from the quantum computing device 2000 (e.g., AC linepower).

The quantum computing device 2000 may include a display device 2006 (orcorresponding interface circuitry, as discussed above). The displaydevice 2006 may include any visual indicators, such as a heads-updisplay, a computer monitor, a projector, a touchscreen display, aliquid crystal display (LCD), a light-emitting diode display, or a flatpanel display, for example.

The quantum computing device 2000 may include an audio output device2008 (or corresponding interface circuitry, as discussed above). Theaudio output device 2008 may include any device that generates anaudible indicator, such as speakers, headsets, or earbuds, for example.

The quantum computing device 2000 may include an audio input device 2024(or corresponding interface circuitry, as discussed above). The audioinput device 2024 may include any device that generates a signalrepresentative of a sound, such as microphones, microphone arrays, ordigital instruments (e.g., instruments having a musical instrumentdigital interface (MIDI) output).

The quantum computing device 2000 may include a GPS device 2018 (orcorresponding interface circuitry, as discussed above). The GPS device2018 may be in communication with a satellite-based system and mayreceive a location of the quantum computing device 2000, as known in theart.

The quantum computing device 2000 may include an other output device2010 (or corresponding interface circuitry, as discussed above).Examples of the other output device 2010 may include an audio codec, avideo codec, a printer, a wired or wireless transmitter for providinginformation to other devices, or an additional storage device.

The quantum computing device 2000 may include an other input device 2020(or corresponding interface circuitry, as discussed above). Examples ofthe other input device 2020 may include an accelerometer, a gyroscope, acompass, an image capture device, a keyboard, a cursor control devicesuch as a mouse, a stylus, a touchpad, a bar code reader, a QuickResponse (QR) code reader, any sensor, or a radio frequencyidentification (RFID) reader.

The quantum computing device 2000, or a subset of its components, mayhave any appropriate form factor, such as a hand-held or mobilecomputing device (e.g., a cell phone, a smart phone, a mobile internetdevice, a music player, a tablet computer, a laptop computer, a netbookcomputer, an ultrabook computer, a personal digital assistant (PDA), anultramobile personal computer, etc.), a desktop computing device, aserver or other networked computing component, a printer, a scanner, amonitor, a set-top box, an entertainment control unit, a vehicle controlunit, a digital camera, a digital video recorder, or a wearablecomputing device.

The following paragraphs provide various examples of the embodimentsdisclosed herein.

Example 1 is a quantum dot device, including: a base; a fin extendingaway from the base, wherein the fin includes a quantum well layer; agate above the fin; and a material on side faces of the fin; wherein thefin has a width between its side faces, and the fin is strained in adirection of the width.

Example 2 may include the subject matter of Example 1, and may furtherspecify that the material includes a liner on the side faces of thefins, and the liner has thickness less than 10 nanometers.

Example 3 may include the subject matter of Example 2, and may furtherspecify that the liner includes nitrogen.

Example 4 may include the subject matter of any of Examples 2-3, and mayfurther specify that the liner includes oxygen.

Example 5 may include the subject matter of any of Examples 2-3, and mayfurther specify that the liner includes silicon.

Example 6 may include the subject matter of any of Examples 2-5, and mayfurther specify that the liner has a thickness that is less than 5nanometers.

Example 7 may include the subject matter of any of Examples 2-6, and mayfurther specify that the material includes a fill material, and theliner is between the fill material and the fin.

Example 8 may include the subject matter of Example 7, and may furtherspecify that the fill material includes nitrogen.

Example 9 may include the subject matter of any of Examples 7-8, and mayfurther specify that the fill material includes silicon.

Example 10 may include the subject matter of any of Examples 1-9, andmay further specify that the fin is a first fin, and the materialincludes a fill material that extends between the first fin and aparallel second fin.

Example 11 may include the subject matter of Example 10, and may furtherspecify that the fill material includes nitrogen.

Example 12 may include the subject matter of any of Examples 10-11, andmay further specify that the fill material includes silicon.

Example 13 may include the subject matter of any of Examples 1-12, andmay further specify that the material contacts side faces of the quantumwell layer.

Example 14 may include the subject matter of any of Examples 1-13, andmay further specify that the fin has a maximum strain at a top surfaceof the fin.

Example 15 may include the subject matter of any of Examples 1-14, andmay further specify that the fin has a maximum strain in the quantumwell layer.

Example 16 may include the subject matter of any of Examples 1-15, andmay further specify that the quantum well layer is at a top surface ofthe fin.

Example 17 may include the subject matter of any of Examples 1-16, andmay further specify that the quantum well layer includes orderedcrystalline silicon or ordered crystalline germanium.

Example 18 may include the subject matter of any of Examples 1-17, andmay further specify that: the gate is a first gate; the first gateincludes a first gate metal; the quantum dot device includes a secondgate above the fin; the second gate includes a second gate metal; and amaterial structure of the second gate metal is different from a materialstructure of the first gate metal.

Example 19 may include the subject matter of Example 18, and may furtherspecify that the quantum well layer has a first strain under the firstgate, a second strain under the second gate, and the first strain isdifferent from the second strain.

Example 20 may include the subject matter of any of Examples 1-19, andmay further specify that the fin has a width between 10 nanometers and30 nanometers.

Example 21 may include the subject matter of any of Examples 1-20, andmay further specify that the fin has a tapered shape that is widestproximate to the base.

Example 22 may include the subject matter of any of Examples 1-21, andmay further specify that the material induces strain in the fin in adirection of the width.

Example 23 is a method of operating a quantum dot device, including:providing electrical signals to one or more first gates above a fin aspart of causing a first quantum well to form in a quantum well layer inthe fin; providing electrical signals to one or more second gates abovethe fin as part of causing a second quantum well to form in the quantumwell layer in the fin; and providing electrical signals to one or morethird gates above the fin to (1) cause a third quantum well to form inthe quantum well layer or (2) provide a potential barrier between thefirst quantum well and the second quantum well; wherein astrain-inducing material is present on side surfaces of the fin.

Example 24 may include the subject matter of Example 23, and may furtherinclude: populating the first quantum well with a quantum dot.

Example 25 may include the subject matter of any of Examples 23-24, andmay further specify that the quantum well layer is at a top surface ofthe fin.

Example 26 is a method of manufacturing a quantum dot device, including:forming a quantum well stack, wherein the quantum well stack includes aquantum well layer; forming a fin from the quantum well stack; andforming a material on side faces of the fin to induce strain across thefin between the side faces.

Example 27 may include the subject matter of Example 26, and may furtherspecify that forming the material on side faces of the fin includesdepositing a fin liner on the fin, wherein the fin liner induces strainin the fin.

Example 28 may include the subject matter of Example 27, and may furtherspecify that forming the material on side faces of the fin includes,after depositing the fin liner, blanket depositing a fill materialaround the fin, wherein the fill material induces strain in the fin.

Example 29 may include the subject matter of Example 27, and may furtherspecify that forming the material on sides of the fin includesdirectionally etching the fin liner.

Example 30 may include the subject matter of Example 26, and may furtherspecify that forming the material on side faces of the fin includesblanket depositing a fill material around the fin, wherein the fillmaterial induces strain in the fin.

Example 31 may include the subject matter of any of Examples 26-30, andmay further include: forming a first gate above the quantum well stack,wherein the first gate includes a first gate metal; and forming a secondgate above the quantum well stack, wherein the second gate includes asecond gate metal, and the second gate metal has a different materialstructure than the first gate metal.

Example 32 may include the subject matter of Example 31, and may furtherspecify that the first and second gates induce differential strain inthe quantum well layer.

Example 33 is a quantum computing device, including: a quantumprocessing device, wherein the quantum processing device includes a fin,the fin includes a quantum well layer, the quantum processing devicefurther includes a plurality of gates above the fin to control quantumdot formation in the fin and a material on side faces of the fin, thefin has a width between the side faces, and the fin is strained in adirection of the width; and a non-quantum processing device, coupled tothe quantum processing device, to control voltages applied to theplurality of gates.

Example 34 may include the subject matter of Example 33, and may furtherinclude: a memory device to store data generated by quantum dots formedin the quantum well layer during operation of the quantum processingdevice.

Example 35 may include the subject matter of Example 34, and may furtherspecify that the memory device is to store instructions for a quantumcomputing algorithm to be executed by the quantum processing device.

Example 36 may include the subject matter of any of Examples 33-35, andmay further include: a cooling apparatus.

Example 37 may include the subject matter of any of Examples 33-36, andmay further specify that the material includes a strain-inducing liner.

Example 38 may include the subject matter of Example 37, and may furtherspecify that the material further includes a strain-inducing fillmaterial on the strain-inducing liner.

Example 39 may include the subject matter of any of Examples 33-38, andmay further specify that the material contacts side faces of the quantumwell layer.

The invention claimed is:
 1. A quantum dot device, comprising: a base; afin extending away from the base, wherein the fin includes a quantumwell layer; a first gate above the fin, wherein the first gate includesa first gate metal; a second gate above the fin, wherein the second gateincludes a second gate metal, and a material structure of the secondgate metal is different from a material structure of the first gatemetal; and a material on side faces of the fin; wherein the fin has awidth between its side faces, the fin is strained in a direction of thewidth, the quantum well layer has a first strain under the first gate, asecond strain under the second gate, and the first strain is differentfrom the second strain.
 2. The quantum dot device of claim 1, whereinthe material includes a liner on the side faces of the fins, and theliner has thickness less than 10 nanometers.
 3. The quantum dot deviceof claim 2, wherein the liner includes nitrogen, oxygen, or silicon. 4.The quantum dot device of claim 2, wherein the material includes a fillmaterial, and the liner is between the fill material and the fin.
 5. Thequantum dot device of claim 4, wherein the fill material includesnitrogen or silicon.
 6. The quantum dot device of claim 1, wherein thefin is a first fin, and the material includes a fill material thatextends between the first fin and a parallel second fin.
 7. The quantumdot device of claim 6, wherein the fill material includes nitrogen orsilicon.
 8. The quantum dot device of claim 1, wherein the materialcontacts side faces of the quantum well layer.
 9. The quantum dot deviceof claim 1, wherein the fin has a maximum strain at a top surface of thefin.
 10. The quantum dot device of claim 1, wherein the fin has amaximum strain in the quantum well layer.
 11. The quantum dot device ofclaim 1, wherein the quantum well layer includes ordered crystallinesilicon or ordered crystalline germanium.
 12. The quantum dot device ofclaim 1, wherein the fin has a tapered shape that is widest proximate tothe base.
 13. A method of manufacturing a quantum dot device,comprising: forming a quantum well stack, wherein the quantum well stackincludes a quantum well layer; forming a fin from the quantum wellstack; and forming a material on side faces of the fin to induce strainacross the fin between the side faces, wherein forming the material onside faces of the fin includes depositing a fin liner on the fin, thefin liner induces strain in the fin, and forming the material on sidesof the fin includes directionally etching the fin liner.
 14. The methodof claim 13, wherein forming the material on side faces of the finincludes, after depositing the fin liner, blanket depositing a fillmaterial around the fin, wherein the fill material induces strain in thefin.
 15. The method of claim 13, wherein forming the material on sidefaces of the fin includes blanket depositing a fill material around thefin, wherein the fill material induces strain in the fin.
 16. A quantumcomputing device, comprising: a quantum processing device, wherein thequantum processing device includes a fin, the fin includes a quantumwell layer, the quantum processing device further includes a pluralityof gates above the fin to control quantum dot formation in the fin and amaterial on side faces of the fin, the fin has a width between the sidefaces, the fin is strained in a direction of the width, the plurality ofgates includes a first gate and a second gate, the quantum well layerhas a first strain under the first gate, the quantum well layer has asecond strain under the second gate, and the first strain is differentfrom the second strain; and a non-quantum processing device, coupled tothe quantum processing device, to control voltages applied to theplurality of gates.
 17. The quantum computing device of claim 16,further comprising: a memory device to store data generated by quantumdots formed in the quantum well layer during operation of the quantumprocessing device.
 18. The quantum computing device of claim 16, whereinthe material includes a strain-inducing liner.
 19. The quantum computingdevice of claim 18, wherein the material further includes astrain-inducing fill material on the strain-inducing liner.
 20. Aquantum dot device, comprising: a base; a fin extending away from thebase, wherein the fin includes a quantum well layer; a first gate abovethe fin; a second gate above the fin; and a material on side faces ofthe fin; wherein the fin has a width between its side faces, the fin isstrained in a direction of the width, the quantum well layer has a firststrain under the first gate, a second strain under the second gate, andthe first strain is different from the second strain.
 21. The quantumdot device of claim 20, wherein the fin has a maximum strain at a topsurface of the fin.
 22. The quantum dot device of claim 20, wherein thefin has a maximum strain in the quantum well layer.
 23. The quantum dotdevice of claim 20, wherein the quantum well layer includes orderedcrystalline silicon or ordered crystalline germanium.
 24. The quantumdot device of claim 20, wherein the quantum well layer includes orderedcrystalline silicon or ordered crystalline germanium.
 25. The quantumdot device of claim 20, wherein the fin has a tapered shape that iswidest proximate to the base.